Cisco Tips & Tricks

November 17, 2009

L2VPN/VPLS-Martini and Kompella

Filed under: bgp, ccie, cisco, MPLS — ciscotips @ 2:24 am

Both Martini-draft and Kompella-draft addressed setting up of a Pseudowire emulation over MPLS in order to offer L2VPN services. These drafts were initial efforts to standardise L2VPN services.

Martini draft was named after a former Cisco employee Luca Martini. Martini draft uses LDP as signalling to setup L2VPN over MPLS backbone. The tradeoff of this draft was auto-discovery.

Kompella draft on the other hand uses BGP for both signalling and auto-discovery to establish fully-meshed pseudo wires (multipoint). Kompella-draft is named after author Keerti Kompella (Juniper Employee).

draft-martini and draft-kompella terms are used as labels for the two different L2VPN services methodologies (LDP Vs BGP for signaling). The actual drafts do not exist in IETF.

In dealing with multipoint-fully meshed topologies in edge routers, draft-martini suffered auto-discovery, to overcome aut0-discovery, it suffered configuration overhead. draft-Kompella claimed to be better scalable because of suto-discovery but with complex signalling whereas draft-martini leverages simplicity.

Martini draft was standardized under RFC 4096 . however it has since been superseded by the Pseudowire Emulation Edge to Edge (PWE3) Working Group specifications described in RFC 4447 and related documents. On the other hand draft-kompella is obsolete and was not standardized..

 RFC 4664 – Framework for Layer 2 Virtual Private Networks (L2VPN), it describes the framework for L2VPNs (VPWS, VPLS and IPLS). This framework is intended to aid in standardizing protocols and mechanisms to support interoperable L2VPNs. Requirements for L2VPNs can be found in RFC 4665 – Service Requirements for Layer 2 Provider-Provisioned Virtual Private Networks.

All this was consolidated, and the L2VPN Working Group produced two separate documents, RFC 4761 and RFC 4762, both offered VPLS but using different signaling protocols:

Kireeti Kompella and Yakov Rekhter published “Virtual Private LAN Service (VPLS) Using BGP for Auto-discovery and Signaling” RFC 4761 in January 2007.

Marc Lasserre and Vach Kompella published “Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling” RFC 4762 in January 2007.

L2VPN services for many vendors uses RFC 4762 -Martini ( with LDP) as a standard for example Alcatel 7450’s uses RFC 4762 as the standard

October 25, 2009

BGP Regular expressions / Public route-servers

Filed under: bgp, ccie, IP Routing — ciscotips @ 5:28 am

I was looking at some older posts at Groupstudy and Dale  posted the link to public route-servers. I agree the best way to practice regular-expressions for CCIE is to use one of the following public route-servers.

From: http://www.cymru.com/Documents/secure-bgp-template.html

 route-views.oregon-ix.net
 ner-routes.bbnplanet.net
 route-server.cerf.net
 route-server.ip.att.net
 route-server.east.attcanada.com
 route-server.west.attcanada.com
 route-server.cbbtier3.att.net
 route-server.gblx.net
 route-server.as5388.net
 route-server.savvis.net
 route-server.colt.net
 route-server.opentransit.net
 route-server.gt.ca
 public-route-server.is.co.za (South African routes only)
 route-server.belwue.de
 route-views.on.bb.telus.com
 route-views.ab.bb.telus.com
 route-server.ip.tiscali.net
 route-server.wcg.net
 route-server.manilaix.net.ph
 route-server.ip.ndsoftware.net
 route-server.utah.rep.net
 route-server.he.net
 zebra.swinog.ch

Just telnet to one of the above route-servers and you can login via guest/anonymous account. There you go and you can use some basic show commands.

August 3, 2009

MPLS, VRF-lite in CCIEv4

Filed under: bgp, ccie, cisco, MPLS, VPNv4, VRF, VRF-lite — ciscotips @ 1:50 pm

Now that I am preparing for version 4 . I started reading MPLS configuration on IOS software by Cisco press. I am not very comfortable with just reading book and doing nothing. I chose this book because it has some mini scenarios which I can simulate on my dynamips home lab.

I liked the book but then I remembered seeing a post by Antonio on group study that he created his own mini scenarios for studying CCIE SP. Although CCIE SP goes pretty beyond on what we need for R&S but I thought it would be a good practice to try some mini scenarios which are relevant for CCIE R&S. I am sharing the links to mini Scenarios and videos made by Antonio.

http://pwp.netcabo.pt/amsoares/dynamips/dynamips.htm

http://pwp.netcabo.pt/amsoares/dynamips2/dynamips2.htm

Thanks to Antonio for his amazing MPLS mini labs and videos.

July 16, 2009

Cisco Learning Network for your CCIE

Filed under: bgp, ccie, cisco, IP Routing, ospf — ciscotips @ 3:20 pm

Excellent resource to master IP routing ( IGP’s and BGP) with following free Lab resources from Cisco Learning Network. These labs are used for training Cisco TAC .

https://cisco.hosted.jivesoftware.com/docs/DOC-1318

You will need a CCO username/password to access these free labs.

Thanks!

June 10, 2009

Cisco Revising CCIE R&S Certification

Filed under: bgp, ccie, cisco, IP Routing, Technology and Software — ciscotips @ 8:10 pm

The upcoming Version 4.0 of Cisco CCIE® Routing and Switching certification will test hands-on troubleshooting, Multiprotocol Label Switching (MPLS), and VPN networking

 

To reflect the growth of the network as a service platform, Cisco is revising the certification requirements for CCIE Routing & Switching (CCIE R&S)–the expert level certification for network engineers. The new requirements were developed with assistance from Cisco enterprise customers and reflect the expectations of employers across industries.

 

The competencies required for CCIE R&S v4.0 certification were released on May 5, 2009, and are available on the Cisco Learning Network under the CCIE R&S v4.0 Written Exam topics and CCIE R&S v4.0 Lab Exam topics. Exams based on the new requirements are scheduled for release on October 18, 2009, and will immediately replace the currently available v3.0 exams. Candidates who plan to take their exams on October 18, 2009, or later should prepare using the new v4.0 exam topics.

 

Both the written and lab exams will be refreshed with new questions and will cover MPLS and VPN networking. The written exam will add scenario-based questions to the multiple choice questions, and the lab will now require hands-on troubleshooting of preconfigured networks, in addition to configuration. Exam duration and pricing will remain the same, with the two-hour written exam at USD$350 and the eight-hour lab at USD$1400.

 

A beta version of the new CCIE R&S v4.0 written exam (351-001) will be available to all customers in the July–August 2009 timeframe at a discounted price of USD$50. An announcement will be made when scheduling begins.

 

Cisco 360 Learning Program Updates Available

Cisco 360 Learning Program components aligned to the new CCIE R&S certification standards will be available on May 11, 2009.  All current students will have access to the new materials throughout their subscription period.  New materials include additional lessons on MPLS and troubleshooting, enhanced coverage of these topics in the instructor-led workshops, an updated Practice Lab Workbook for self-paced practice, and new Performance Assessments that gauge skill level and offer mentoring feedback.

 

CCIE Assessor, the first CCIE R&S practice lab, will be retired on June 5, 2009, and will be replaced by the 10 eight-hour assessment labs available through the Cisco 360 Learning Program. Find out more

 

Frequently Asked Questions

1  –  Q: What exactly is being changed on the CCIE R&S written exam?

 

A: The CCIE R&S v4.0 written exam will be refreshed with new questions to reflect the current job role expectations of employers. Scenario-based questions will be added to the multiple choice questions. New topics include the skills associated with planning and evaluating network changes, implementing MPLS, Layer 3 VPN, IPv6, EIGRP and multicast; and configuring performance-based routing.  More information is available on the CCIE Written Exam Overview page.

 

 

2  –  Q: What exactly is being changed on the CCIE R&S lab exam?

A: The CCIE R&S v4.0 lab exam will be refreshed with new questions to reflect the current job role expectations of employers. The equipment in the testing lab will be updated with Cisco 1800 and 3800 Series Integrated Services Routers running Cisco IOS® Software Version 12.4(T) and Cisco Catalyst® 3560 Series Switches running Cisco IOS Version 12.2 Advanced IP Services. The biggest change will be the testing of hands-on troubleshooting for the first two hours of the eight-hour exam. Candidates will be presented with a series of trouble tickets for preconfigured networks, and they will need to diagnose and resolve the network fault or faults—a realistic and challenging job task. Candidates who finish the troubleshooting section early can move on to the configuration section, but they will not be allowed to go back to the troubleshooting section, since their equipment will need to be reinitialized for the configuration portion of the exam.

To make time for new material, CCIE R&S v4.0 exams will put less emphasis on equipment operation and concepts generally understood at the professional level. These skills are still assumed, but will not be the sole objective of CCIE test questions. Go to the Lab Exam Study/Learn section for more information.

 

 

3  –  Q: Now that the CCIE R&S v4.0 has been announced, can I still take the CCIE R&S v3.0 exam? How long will it be valid?

 

A: The CCIE R&S v3.0 written exam will be available through October 17, 2009, at all Pearson VUE testing centers. Passing the v3.0 written exam qualifies a candidate to take any available version of the CCIE R&S lab exam. As with all CCIE written exams, a passing score on v3.0 written exam will remain valid for three years, as long as the candidate attempts the lab exam once within the first 18 months. If the lab is not attempted, the written exam becomes invalid and the candidate will have to retest using whatever written exam is available at that time.

 

 

4  –  Q: If I take the CCIE R&S written beta test in July or August 2009, will I still be able to schedule the CCIE R&S v3.0 lab exam?

 

A: Scores on CCIE written beta tests are not available until 4 to 6 weeks after the close of the beta period. At this time, there is no guarantee the CCIE R&S v3.0 lab exam will still be available when a beta test candidate receives his or her score. Beta testers should plan on taking the CCIE R&S v4.0 lab test to achieve certification.

 

 

5  –  Q: If I don’t pass the CCIE R&S v4.0 written beta exam, can I take it again in five days?

 

A: No, a candidate can only take a CCIE written beta test once during the beta testing period.

 

 

 

6  –  Q: Will there be any changes to the recently-added Core Knowledge portion of the exam, the part with the short-answer questions?

 

A: The questions in the Core Knowledge section of the lab exam may cover any area on the CCIE R&S v4.0 Lab Exam topics.

 

 

 

7  –  Q: What can a candidate expect in the troubleshooting portion of the lab exam?

 

A: Troubleshooting is allotted two of the eight hours required for the CCIE lab exam. Candidates will be presented with a series of trouble tickets for preconfigured networks and will need to diagnose and resolve the fault or faults. As with previous CCIE labs, the network will need to be up and running for the candidate to receive credit.  Candidates who finish the troubleshooting section early can move on to the configuration section, but they will not be allowed to go back to the troubleshooting section.

 

 

8  –  Q: Does a candidate have to pass both the troubleshooting and configuration sections in order to pass the entire CCIE R&S v4.0 lab exam and earn a CCIE?

 

A: Candidates will receive a single pass/fail grade on the entire exam, including both configuration and troubleshooting. Failing score reports will give an indication of where the candidate scored lower, to help the candidate prepare for another attempt.

 

 

9  –  Q: Will the CCIE R&S mobile lab exam also be updated?

 

A: Yes, CCIE R&S mobile labs use the same lab version as Cisco office locations, and they will switch to the v4.0 lab exam on October 18, 2009 as well.

 

 

10  –  Q: Which exam will be used for recertification?

 

A: As of October 18, 2009, CCIEs who take the CCIE R&S written exam for recertification will be given the v4.0 exam and should prepare using the exam topics found on the Cisco Learning Network.

 

 

11  –  Q: Are the previous Cisco 360 components applicable to the CCIE R&S v4.0 exams? Should candidates studying for CCIE R&S v4.0 exams wait for the new Cisco 360 materials to begin work?

 

A: The learning components available at first launch of Cisco 360 are still relevant to candidates studying for the CCIE R&S v4.0 certification exams. No Cisco 360 Learning Program components are being retired.  There is no need for candidates to wait for revised Cisco 360 material to begin their study and practice. The subscription model ensures that Cisco 360 customers can take advantage of all new content as it is released and do not need to wait.

February 8, 2009

BGP at 18

Filed under: bgp, ccie, cisco, Router — ciscotips @ 11:49 pm

 

October 24, 2008

Day 3, 4 and 5 of Narbik’s Bootcamp

Filed under: bgp, ccie, IP Routing, QOS, Technology and Software — ciscotips @ 6:22 pm

Sorry for posting late, Narbiks bootcamp was fun. Its worth attending his bootcamp if you are somewhere in the mid-tier of your CCIE preparation. Narbik recommends to cover Soups-to-nuts before you attend his bootcamp and he is right., otherwise it can be too much of information for you in 5 Days. Here is what he covered in last three days.

Day 3:- BGP

It was a big day for me. Day 3 is a BGP day, youy have  almost 200 pages worth of BGP labs. Narbik’s BGP  lecture style is totally different then the conventional CCIE Instructors. He doesn’t start BGP with Attributes or BGP states. He attacks on BGP optimization and then buiold you towards attributes and other advance topics. Simply awesome. He will start with MSS ( Maximum segment size) , Scan time, Advertising Interval and then take you to Memory pools, templates and Peer-groups. At last he will talk about BGP states, Aggregation, Attributes and some awesome route-filtering techniques. I will say that was my best BGP class.

Day 4:- RIPv2 and QoS

Another big day which was dedicated to Qos and 2 hours worth of lecture for RIP v2.  He showed what RIPv2 is worth of. People normally ignore RIP but if you know what all you can do with RIP. You will never be disappointed to use it for your small size network. He covered optimization, RIP updates,Filtering,redistribution,authentication  building it on some advanced scenarios.

Qos:- Qos

Qos was never my strong topic, although I am using it regularly in my job but I always struggled on few advanced topics. I should not have a problem in Qos after attending Narbik’s lecture.  Narbik started Qos with Queuing. He covered, CBWFQ, LLQ, filtering,CBWRED,Shaping, CAR,policing and SRR. Pretty good lecture indeed!

FInal Day ( Day 5 Multicast and CCIE lab tips).

Narbik covered multicast Addressing, Delievery Methods, Manipulating MCast Traffic, Dense,sparse modes, MSDP,ANycast and udp helper. I still have to work on Multicast labs but I am sure  I can practice on it  and grasp what I need most for my Lab.

As I am going through Narbik’s Advance 6 volume CCIE workbooks, I will try to post tips and tricks on various technologies going forward.

October 10, 2006

Cisco Simulator for CCIE’s

Filed under: bgp, cisco, IP Routing, ospf, QOS — ciscotips @ 8:17 pm

what cisco simulator !!! Are you crazy… No I am not!

My frenz never believed me that I am using a cisco simulator for my CCIE lab practice. My simulator can support direct images of 7200 and now 3600 series. Hard to believe!

check this out

http://www.ipflow.utc.fr/blog/

October 5, 2006

MPLS VPN

Filed under: bgp — ciscotips @ 6:15 pm

An excellent paper to understand MPLS VPN’s

http://www.cse.iitb.ac.in/~varsha/allpapers/network-misc/mplsvpns.pdf

September 20, 2006

BGP- FAQ from Cisco’s website

Filed under: bgp, cisco, IP Routing, Router — ciscotips @ 8:52 pm

A pretty useful document for better understanding of BGP. 

 

Introduction

This document contains frequently asked questions (FAQs) about Border Gateway Protocol (BGP).

Q. How do I configure BGP with the use of a loopback address?A. The use of a loopback interface ensures that the neighbor stays up and is not affected by

malfunctioning hardware.

BGP uses the IP address configured on the physical interface directly connected to the BGP

peer as the source address when it establishes the BGP peering session, by default. Issue the

neighbor <ip address> update−source <interface> command in order to change this

behavior and configure the BGP that speaks to the router to establish peering with the use of a

loopback address as the source address.

Refer to Sample Configuration for iBGP and eBGP With or Without a Loopback Address for

more information.

Q. What is the order of preference of attributes when some or all are

applied to one neighbor in BGP?

A. The order of preference varies based on whether the attributes are applied for inbound

updates or outbound updates.

For inbound updates the order of preference is:

route−map 1.

filter−list 2.

prefix−list, distribute−list 3.

For outbound updates the order of preference is:

prefix−list, distribute−list 1.

filter−list 2.

route−map 3.

Note: The attributes prefix−list and distribute−list are mutually exclusive, and only one command (neighbor prefix−list or neighbor distribute−list) can be applied to each inbound

or outbound direction for a particular neighbor.

Q. What does a next hop of 0.0.0.0 mean in the show ip bgp command

output?

A. A network in the BGP table with a next hop address of 0.0.0.0 means that the network is

locally originated via redistribution of Interior Gateway Protocol (IGP) into BGP, or via a

network or aggregate command in the BGP configuration.

Q. What are the well known communities of the BGP community

attribute?

A. The community attribute is a transitive, optional attribute designed to group destinations in

a certain community and apply certain policies (such as accept, prefer, or redistribute). This

table shows the well known BGP communities.

Community Description
Local-AS Use in confederation scenarios to prevent sending packets outside the local autonomous system (AS).
no-export Do not advertise to external BGP (eBGP) peers. Keep this route within an AS.
no-advertise Do not advertise this route to any peer, internal or external.
none Apply no community attribute when you want to clear the communities associated with a route.
internet Advertise this route to the internet community, and any router that belongs to it.

.

Q. What formats can I use to configure the BGP community attribute?

A. In Cisco IOS® Software release 12.0 and later, you can configure communities in three

different formats called decimal, hexadecimal, and AA:NN. By default, IOS uses the older

decimal format. In order to configure and display in AA:NN, where the first part is the AS

number and the second part is a 2−byte number, use the ip bgp new−format global

configuration command.

Note: Although the community attribute can be represented in decimal, hexadecimal, or

AA:NN, it is still a 32−bit number. For example, any of these three configuration commands

specify the community 30:20 (AS 30, number 20):

set community 30:20 ¨

set community 0x1E0014 ¨

set community 1966100 ¨

Regardless of which command you use, the community displayed in the router configuration

file and the BGP table is 30:20.

Refer to the Community Attribute section of BGP Case Studies, and Using BGP Community

Values to Control Routing Policy in Upstream Provider Network for more information.

Q. How does BGP behave differently with auto−summary enabled or

disabled?

A. Auto−summary behavior has changed across Cisco IOS releases. Initially, auto−summarywas enabled by default. However, with Cisco bug ID CSCdu81680 ( registered customers only)

this behavior has changed. In the latest Cisco IOS, auto−summary is disabled by default.

When auto−summary is enabled, it summarizes the locally originated BGP networks to their

classfull boundaries. (Auto−summary is enabled by default in BGP). When auto−summary is

disabled, the routes introduced locally into the BGP table are not summarized to their

classfull boundaries. When a subnet exists in the routing table and the following three

conditions are satisfied, then any subnet of that classfull network in the local routing table

will prompt BGP to install the classfull network into the BGP table.

Classfull network statement for a network in the routing table ¨

Classfull mask on that network statement ¨

Auto−summary enabled ¨

For example, if the subnet in the routing table is 75.75.75.0 mask 255.255.255.0, and you

configure network 75.0.0.0 under the router bgp command, and auto−summary is enabled,

BGP introduces the classfull network 75.0.0.0 mask 255.0.0.0 in the BGP table.

If these three conditions are not all met, then BGP does not install any entry in the BGP table

unless there is an exact match in the local routing table.

Note: If the AS that performs BGP does not own the complete classfull network, Cisco

recommends that you disable auto−summary using the no auto−summary command under

router bgp.

Q. How can I verify if a BGP router announces its BGP networks and

propagates them to the global BGP mesh?

A. Use these commands to check if the IP blocks are announced to the directly connected

ISP:

The show ip bgp neighbors [address] advertise−routes command shows which

messages are being sent.

¨

The show ip bgp neighbors [address] routes command shows which messages are

being received.

¨

Note: The show ip bgp neighbors [address] advertise−routes command does not take into

account any outbound policies you may have applied. In future Cisco IOS versions the

command output will be changed to reflect the outbound policies.

In order to verify how the IP blocks get propagated to the global BGP mesh via the directly

connected ISP, log onto a route server on the Internet and look for the BGP entries of the

prefix in the route server.

Q. When and how should I reset a BGP session?

A. Clear a BGP session when you change the inbound/outbound policy for this session. Use

the clear ip bgp x.x.x.x soft out command to clear a BGP session in order to bring outboundpolicy changes into effect. Use the

clear ip bgp x.x.x.x command in order to clear a BGP

session to bring inbound policy changes into effect. If the neighbor has the soft

reconfiguration capability, you can use the clear ip bgp x.x.x.x soft in command.

Note: With Cisco IOS Software Release 12.0 and later, a new BGP Soft Reset Enhancement

feature is introduced. Refer to BGP Soft Reset Enhancement for more information.

Q. When I perform MD5 Authentication for BGP through a PIX, is there

anything special that needs to be done on the PIX?

A. Yes. When a BGP ‘neighbor … password …’ is configured, MD5 authentication is used on

the TCP psuedo−IP header, TCP header, and data (refer to RFC 2385 ). TCP uses this data,

which includes the TCP sequence and ACK numbers, and the BGP neighbor password, to

create a 128−bit hash number. The hash number is included in the packet in a TCP header

option field. By default, the PIX offsets the sequence number by a random value per TCP

flow. On the sending BGP peer, TCP uses the original sequence number to create the 128−bit

MD5 hash number and includes this hash number in the packet. When the receiving BGP peer

gets the packet, TCP uses the PIX modified sequence number to create a 128−bit MD5 hash

number and compares it to the hash number included in the packet. Because the TCP

sequence value was changed by the PIX, the hash is differentTCP on the BGP neighbor

drops the packet and logs an MD5 failed message similar to this:

%TCP−6−BADAUTH: Invalid MD5 digest from 10.28.0.9:1778 to 10.156.50.10:179

Use the norandomseq keyword to solve this problem and stop the PIX from offsetting the

TCP sequence number with this command:

static (inside,DMZ−ICE) 10.0.0.0 10.0.0.0 netmask 255.0.0.0 norandomseq

Q. What is an autonomous system (AS) number and how do I obtain

one?

A. AS numbers are globally unique numbers that are used to identify ASes, and which enable

an AS to exchange exterior routing information between neighboring ASes. An AS is a

connected group of IP networks that adhere to a single and clearly defined routing policy.

There are a limited number of available AS numbers. Therefore, it is important to determine

which sites require unique AS numbers and which do not. Sites that do not require a unique

AS number should use one or more of the AS numbers reserved for private use, which are in

the range from 64512 to 65535. Access the AS Number Registration Services Website to

obtain an AS number.

Q. What is the BGP path selection criteria?

A. BGP path selection criteria is documented in BGP Best Path Selection Algorithm.

Q. What is the difference between always−compare−med and

deterministic−med?

A. A complete explanation of the differences between these commands is documented in

How the bgp deterministic−med Command Differs from the bgp always−compare−med

Command.

Q. Do internal BGP sessions modify the next hop?

A. Internal BGP (iBGP) sessions preserve the next hop attribute learned from eBGP peers.

This is why it is important to have an internal route to the next hop. The BGP route is

otherwise unreachable. In order to make sure you can reach the eBGP next hop, include the

network that the next hop belongs to in the IGP or use the next−hop−self neighbor command

to force the router to advertise itself, rather than the external peer, as the next hop. Refer to

the BGP Nexthop Attribute section of BGP Case Studies for a more detailed explanation.

Q. Do eBGP sessions between confederations modify the next hop?

A. No, eBGP sessions between confederation sub−ASes does not modify the next hop

attribute. All iBGP rules still apply to have the whole AS behave as a single entity. The

metric and local preference values also remain unaltered among confederation eBGP peers.

Refer to the BGP Confederation section of BGP Case Studies for more information about

confederations.

Q. In eBGP sessions, which IP address is sent as the next hop?

A. In eBGP peering, the next hop is the IP address of the neighbor that announces the route.

However, when the route is advertised on a multi−access media (such as Ethernet or Frame

Relay), the next hop is usually the IP address of the router interface connected to that media,

which originated the route. Refer to the BGP Nexthop Attribute of BGP Case Studies for a

more detailed explanation.

Q. Does the route reflector change the next hop attribute of a reflected

prefix?

A. By default, the next hop attribute is not changed when a prefix is reflected by route reflector. However, you can use the neighbor next−hop−self command to change the

attribute of the next hop for prefixes reflected from an eBGP peer to any route reflector client.

Q. How can I announce a prefix conditionally to one ISP only when I lose

the connection to my primary ISP?

A. BGP advertises routes from its BGP table to external peers by default. The BGP

conditional advertisement feature provides additional control of route advertisement

depending on the existence of other prefixes in the BGP table. Normally, routes are

propagated regardless of the existence of a different path. The BGP conditional advertisement

feature uses the non−exist−map and advertise−map configuration commands to track routes

by the route prefix. If a route prefix is not present in the non−exist−map command, the routespecified by the

advertise−map command is announced. Refer to the Configuring BGP

Conditional Advertisement section of Configuring BGP for more information.

Q. How much memory should I have in my router to receive the

complete BGP routing table from my ISP?

A. The amount of memory required to store BGP routes depends on many factors, such as the

router, the number of alternate paths available, route dampening, community, the number of

maximum paths configured, BGP attributes, and VPN configurations. Without knowledge of

these parameters it is difficult to calculate the amount of memory required to store a certain

number of BGP routes. Cisco typically recommends a minimum of 128 MB of RAM in the

router to store a complete global BGP routing table from one BGP peer. However, it is

important to understand ways to reduce memory consumption and achieve optimal routing

without the need to receive the complete Internet routing table. Refer to Achieve Optimal

Routing and Reduce BGP Memory Consumption for more detailed information.

Q. What are the benefits of configuring BGP peer groups?

A. The major benefit of specifying a BGP peer group is that it reduces the amount of system

resources (CPU and memory) used in an update generation. It also simplifies BGP

configuration since it allows the routing table to be checked only once, and updates to be

replicated to all other in−sync peer group members. Depending on the number of peer group

members, the number of prefixes in the table, and the number of prefixes advertised, this can

significantly reduce the load. Cisco recommends that you group together peers with identical

outbound announcement policies. Refer to BGP Peer Groups for more detailed information.

Q. What is synchronization, and how does it influence BGP routes

installed in the IP routing table?

A. If your AS passes traffic from another AS to a third AS, BGP should not advertise a route

before all routers in your AS learn about the route via IGP. BGP waits until IGP propagates

the route within the AS and then advertises it to external peers. A BGP router with

synchronization enabled does not install iBGP learned routes into its routing table if it is not

able to validate those routes in its IGP. Disabling synchronization using the no synchronization command under router bgp prevents BGP from validating iBGP routes in

IGP. Refer to BGP Case Studies: Synchronization for a more detailed explanation.

Q. How do I know which Cisco IOS software release supports a

particular BGP feature?

A. Use the Cisco IOS Software Advisor ( registered customers only) to quickly find which Cisco

IOS software release supports your feature.

Q. How can I set the Multi Exit Discriminator (MED) value on prefixes

advertised to eBGP neighbors to match the IGP next hop metric?

A. The set metric−type internal route−map configuration command causes BGP to

advertise a MED that corresponds to the IGP metric associated with the next hop of the route.

This command is available in Cisco IOS Software Release 10.3 and later.

Q. What is the default BGP ConnectRetry timer, and is it possible to tune

the BGP ConnectRetry timer?

A. The default BGP ConnectRetry timer is 120 seconds. Only after this time passes does the

BGP process check to see if the passive TCP session is established. If the passive TCP

session is not established, then the BGP process starts a new active TCP attempt to connect to

the remote BGP speaker. During this idle 120 seconds of the ConnectRetry timer, the remote

BGP peer can establish a BGP session to it. Presently the Cisco IOS ConnectRetry timer

cannot be changed from its default of 120 seconds.

Q. What does r RIB−Failure mean in the show ip bgp command output?

R1> show ip bgp

BGP table version is 5, local router ID is 200.200.200.1

Status codes: s suppressed, d damped, h history, * valid, > best, i − internal,

r RIB−failure

Origin codes: i − IGP, e − EGP, ? − incomplete

Network Next Hop Metric LocPrf Weight Path

r> 6.6.6.0/24 10.10.13.3 0 130 0 30 i

*> 7.7.7.0/24 10.10.13.3 0 125 0 30 i

When BGP tries to install the bestpath prefix into Routing Information Base (RIB) (for

example, the IP Routing table), RIB might reject the BGP route due to any of these reasons:

Route with better administrative distance already present in IGP. For example, if a

static route already exists in IP Routing table.

¨

Memory failure. ¨

The number of routes in VPN routing/forwarding (VRF) exceeds the route−limit

configured under the VRF instance.

¨

In such cases, the prefixes that are rejected for these reasons are identified by r RIB Failure in the show ip bgp command output and are not advertised to the peers. This

feature was first made available in Cisco IOS Software Release 12.2(08.05)T.

Q. How can I redistribute internal BGP (iBGP) learned default−route

(0.0.0.0/0) route into EIGRP/OSPF/IS−IS?

A. The redistribution of iBGP routes into Interior Gateway Protocol (IGP)Enhanced Interior

Gateway Routing Protocol/Open Shortest Path First/Intermediate System−to−Intermediate

System (EIGRP/OSPF/IS−IS)can cause routing loops within the Autonomous System,

which is not recommended. By default, iBGP redistribution into IGP is disabled. Use the bgpredistribute−internal command to enable redistribution of iBGP routes into IGP.

Precautions should be taken to redistribute specific routes using route−maps into IGP. A

sample configuration for redistributing a iBGP learned default route 0.0.0.0/0 into EIGRP is

shown in this output. Configurations for OSPF/IS−IS are similar.

router bgp 65345

[…]

bgp redistribute−internal

!

router eigrp 10

[…]

redistribute bgp 65345 route−map check−def

!

ip prefix−list def−route seq 5 permit 0.0.0.0/0

!

route−map check−def permit 10

match ip address prefix−list def−route

 

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