# The use of the update-source command

**URL:** <https://forum.networklessons.com/t/the-use-of-the-update-source-command/7418>\
**Category:** BGP\
**Created:** [June 12, 2019, 10:06pm UTC](https://forum.networklessons.com/t/the-use-of-the-update-source-command/7418 "2019-06-12T22:06:33Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![gaby.ochoa](https://cdn-forum.networklessons.com/letter_avatar_proxy/v4/letter/g/f9ae1b/32.png) [@gaby.ochoa](https://forum.networklessons.com/u/gaby.ochoa)\
**Post date:** [June 12, 2019, 10:06pm UTC](https://forum.networklessons.com/t/the-use-of-the-update-source-command/7418/1 "2019-06-12T22:06:33Z")

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Hello,  
I am a little confused as to the purpose of the the update-source command in BGP. In the example from the Internal BGP lesson, Rene says that the update-source command is used to specify that we will use the loopback interfaces as the source for the IBGP session.

R4(config-router)# neighbor 2.2.2.2 update-source loopback 0

Does this mean that R4 will be sourcing from R2’s loopback, meaning the neighbor’s loop back? or does it refer to R4’s loopback? I am not clear on this. Can someone please explain? Thanks!

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**Author:** ![sales2161](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/sales2161/32/1432_2.png) [@sales2161](https://forum.networklessons.com/u/sales2161)\
**Post date:** [June 13, 2019, 12:53am UTC](https://forum.networklessons.com/t/the-use-of-the-update-source-command/7418/2 "2019-06-13T00:53:05Z")

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Gaby,

let’s start from fundamentals; by default when BGP is establishing the adjacency with another neighbor, that relationship will be formed using the IP address of the outgoing/closet interface to your neighbor. However this design might cause issues in some design.

Take a look at this topology : **R1** fa0/1-2=========== fa0/1-2 **R2** , R1 is connected to R2 via two interfaces for redundancy. R1 will use one interface to form the neighborship, let’s say fa0/1 in this case. If Fa0/1 goes down for some reason, our BGP relationship will go down immediately then another session will start using the 2nd interface. On a production network, this will definitely introduce an outage while another neighborship is forming.

To overcome this outage in the future, we can create a Loopback interface on our local router, then use it as the source of our TCP session while establishing neighborship by using `neighbor x.x.x.x update-source Loopback x` command.

**Now I go back to your question:**  
R4(config-router)# neighbor 2.2.2.2 update-source loopback 0

> [@gaby.ochoa](#):
>
> Does this mean that R4 will be sourcing from R2’s loopback, meaning the neighbor’s loop back? or does it refer to R4’s loopback?

Can you now try to answer the question? if not, let me know then @lagapidis or @ReneMolenaar might explain better

Regards.

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<div class="post-metadata">

**Author:** ![gaby.ochoa](https://cdn-forum.networklessons.com/letter_avatar_proxy/v4/letter/g/f9ae1b/32.png) [@gaby.ochoa](https://forum.networklessons.com/u/gaby.ochoa)\
**Post date:** [June 13, 2019, 1:54am UTC](https://forum.networklessons.com/t/the-use-of-the-update-source-command/7418/3 "2019-06-13T01:54:48Z")

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thank you so much for this explanation. It makes perfect sense.  
Regards