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New Member

EBGP and update propagated to IBGP neighbors

For IBGP routers to learn about all BGP routes inside the AS, they must connect to every other IBGP router in a full mesh IBGP mesh.

When a BGP router receives routing update from an EBGP neighbor, the update is propagated to all IBGP neighbors. The same is not true for routing update received via an IBGP neighbor.

Now my query if a BGP router (Let us say R2 within AS 200) receives routing update from an EBGP neighbor (let us say R6 within AS600) , the update is propagated to all IBGP neighbors (our case within AS 200), Will this update be propagated to all IBGP speakers within AS 200, even though if there is no full mesh between them ( IBGP speakers)????

2 ACCEPTED SOLUTIONS

Accepted Solutions
Cisco Employee

Re: EBGP and update propagated to IBGP neighbors

The router receiving the prefix from the eBGP peer in AS600 will propagate it to all of its iBGP peers. In turn, these peers will not propagate the prefix to any of their iBGP peers, hence the need for a iBGP full mesh, RR or confederation.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Silver

Re: EBGP and update propagated to IBGP neighbors

Zillah,

Hello and nice to meet you.

My interpretation of your question is as follows. You are receiving updates from R6 in AS600. The updates come into eBGP neighbor R2 (AS200). Does R2 propagate these prefixes to all of it's iBGP neighbors, meaning all routers which iBGP peer directly with R2 in AS200 ?

If this is your qtn the ans is - Yes it will.

However, if the iBGP neigbors of R2 does not directly peer with R2 then the ans in 'NO' and you will need to configure 'Route Reflectors' or 'Confederations' to achieve the desired result. Our learned friend hritter has already pointed out.

hth,

Ajaz Nawaz

3 REPLIES
Cisco Employee

Re: EBGP and update propagated to IBGP neighbors

The router receiving the prefix from the eBGP peer in AS600 will propagate it to all of its iBGP peers. In turn, these peers will not propagate the prefix to any of their iBGP peers, hence the need for a iBGP full mesh, RR or confederation.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Silver

Re: EBGP and update propagated to IBGP neighbors

Zillah,

Hello and nice to meet you.

My interpretation of your question is as follows. You are receiving updates from R6 in AS600. The updates come into eBGP neighbor R2 (AS200). Does R2 propagate these prefixes to all of it's iBGP neighbors, meaning all routers which iBGP peer directly with R2 in AS200 ?

If this is your qtn the ans is - Yes it will.

However, if the iBGP neigbors of R2 does not directly peer with R2 then the ans in 'NO' and you will need to configure 'Route Reflectors' or 'Confederations' to achieve the desired result. Our learned friend hritter has already pointed out.

hth,

Ajaz Nawaz

New Member

Re: EBGP and update propagated to IBGP neighbors

Hi Ajaz

"You are receiving updates from R6 in AS600. The updates come into eBGP neighbor R2 (AS200)."

Yes, this is what I meant.

"Does R2 propagate these prefixes to all of it's iBGP neighbors, meaning all routers which iBGP peer directly with R2 in AS200 ?"

I see.

"However, if the iBGP neigbors of R2 does not directly peer with R2 then the ans in 'NO' and you will need to configure 'Route Reflectors' or 'Confederations' to achieve the desired result."

I see.

"Our learned friend hritter has already pointed out"

I am greatful to you and hritter.

Thanks for both of you

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