05-23-2016 10:52 AM - edited 03-05-2019 04:04 AM
When would you want to make your BGP neighbor their loopback as opposed to your neighbor's connected interface?
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05-23-2016 11:13 AM - last edited on 08-04-2022 02:33 AM by Translator
It depends if you are forming an IBGP neighborship or EBGP neighborship.
With IBGP, it is preferable to peer over loopback interface. This is so because, loopback is an always UP interface (unless its manually shutdown) and if a physical link goes up, there might be an alternate path via IGP to reach the loopback. Thus the BGP session will not go down vs if it is over a physical interface.
With EBGP session, usually the peerings are with provider and over a public IP. Thus the neighborship is established over physical interface. But for security reasons, the peering can be established over loopback with two conditions in mind:
- loopback to loopback/physical interface reachability is there between the two peering devices
- proper ebgp-multihop
is configure or if the peering is between two directly connected router over loopback, then
disable-connected-check
command can be configured for the neighbor.
Hope this answers your question.
Regards
Vinit
05-23-2016 11:13 AM - last edited on 08-04-2022 02:33 AM by Translator
It depends if you are forming an IBGP neighborship or EBGP neighborship.
With IBGP, it is preferable to peer over loopback interface. This is so because, loopback is an always UP interface (unless its manually shutdown) and if a physical link goes up, there might be an alternate path via IGP to reach the loopback. Thus the BGP session will not go down vs if it is over a physical interface.
With EBGP session, usually the peerings are with provider and over a public IP. Thus the neighborship is established over physical interface. But for security reasons, the peering can be established over loopback with two conditions in mind:
- loopback to loopback/physical interface reachability is there between the two peering devices
- proper ebgp-multihop
is configure or if the peering is between two directly connected router over loopback, then
disable-connected-check
command can be configured for the neighbor.
Hope this answers your question.
Regards
Vinit
10-17-2017 08:28 AM - last edited on 08-04-2022 02:36 AM by Translator
Hi Vinit,
I have similar kind of situation while using
disable-connected-check
command.
Is it possible to form neighborship between two routers R1 and R2 , where R1 is having
neighbor
command with IP address of physical interface of R2 and
R2 have
neighbor
command with address of Loopback Interface of R1.
On R1
router bgp 100
neighbor 192.168.12.2 remote-as 200 --> 192.168.12.2 is the Physical interface IP of R2
On R2
router bgp 200
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 update-source Loopback0 --> 1.1.1.1 is the loopback of R1
Will it work in any ways or does disable-connected-check will help?
10-18-2017 01:59 AM
Hi Vinit,
Thanks for the quick reply.
I agree with you Sir but in my case I want to establish EBGP neighborship and the requirement is like
on one router its is loopback int addr and on other end router it is physical int addr onto which I am forming neighborship.If it is possible then also I do not have to use Ebgp-Multihop.
Thanks
Ritesh
05-23-2016 11:15 AM
Loopback use case:
- iBGP neighbors with multiple direct L2 connections: This is an ideal for peering between loopbacks since they can use either ethernet interface.
- Multiple T1's between you and ISP would be an ebgp multihop scenario between loopbacks.
Connected interface:
- eBGP to your service providers.
- iBGP only one interface between routers.
Things like that.
best regards,
tim
05-23-2016 12:00 PM - last edited on 08-04-2022 10:33 PM by Translator
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Posting
The other posters have well answered how loopbacks or directly connected interfaces are typically used. However, I did want to mention, when using iBGP and loopbacks, you may want to also use
next-hop-self
to have the loopback passed to its iBGP peers as BGP's
next hop address too
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