BGP address family

Unanswered Question
Jul 9th, 2008

hai,

iam working with an ISP(VPN),so there is PE-CE setup is availiable and the protocol running is eBGP.So for a particular vrf address family configuraton commands like "no synchronisation" "bgp redistribute internal " are used in the PE.The PE-P-P-PE ospf protocol is used with MPLS switching technology.

cud u please clear me what is this commands inferes...???

I have this problem too.
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lee.reade Wed, 07/09/2008 - 21:37

Hi,

Sorry its not really clear what you are asking for help on, could you provide more information?

Thanks

LR

mahesh_kv3@yahoo.com Wed, 07/09/2008 - 23:16

Hai,

I was bit in a hurry when am writing the first one ,extremely sorry for that and thanx for showing the interrest for this problem

Am working for a MPLS vpn which is having a core backbone made of gsr routers(includes Provider and Provider Edge routers)these PE routers which is connected to the CE(customer Edge router).in between this eBGP protocols will run (like bgp,ospf in the CE will advertise towards CE and redistribute in PE to bgp ).Inbetween all PE routers iBGP protocolis runing(with RR)

what ever the advertisements are coming from the customer Edge router it will redidtribute in to BGP routes.(eBGP pro running bet PE and CE for each customer we will give each vrf and for each ver we will form an address family(routing instance) in the PE router so am giving you one example below

address-family ipv4 vrf vrf_3209

redistribute connected

redistribute ospf 1022 vrf vrf_3209 match internal external 1 external 2

redistribute ospf 1016 vrf vrf_3209 match internal external 1 external 2

no auto-summary

no synchronization

bgp redistribute-internal

exit-address-family

so in this the commands like "no synchronisation " and "bgp redistribute -internal" is used for what purpose .

hope this will work for you .please help me to clear ma doubt

thanx

lee.reade Wed, 07/09/2008 - 23:27

Hi,

The no sync command is default now in IOS, and can be ignored, basically BGP, in the old days, would not use a BGP route learned route unless it had also been learned via an IGP, ie ospf/eigrp etc, however these days, this is turned off.

You can read more about this here, but as mentioned you can ignore this.

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a00800949e8.shtml

The redistribute internal command is used when you have BGP learned routes from iBGP peers, and you want to redistributed these into the IGP, like ospf/eigrp that is used between iBGP peers, say for example not all routers in your network run iBGP so they wont have all the BGP routes, so you need to redistribute iBGP learned routes for this. But again, in MPLS VPN setup, you can ignore this, and even remove the command from the config, as its not needed, as the routes are not learned from BGP but from IGP, ie like ospf in your case.

HTH

LR

guruprasadr Thu, 07/10/2008 - 03:40

Hi Mahesh, [Pls RATE all Informative POST]

Using the Redistribute OSPF Command under BGP Process, you are allowing to both E1 & E2 routes of OSPF also to get redsitributed via BGP process.

About Synchronization:

=======================

If BGP synchronization is enabled, there must be a match for the prefix in the IP routing table in order for an internal BGP (iBGP) path to be considered a valid path. BGP synchronization is enabled by default in Cisco IOS® Software. If the matching route is learned from an Open Shortest Path First (OSPF) neighbor, its OSPF router ID must match the BGP router ID of the iBGP neighbor. Most users prefer to disable synchronization with use of the no synchronization BGP subcommand.

Note: Synchronization is disabled by default in Cisco IOS Software Release 12.2(8)T and later.

Hope I am Informative.

Pls RATE if HELPS

Best Regards,

Guru Prasad R

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