# BGP Backdoor Routes

**URL:** <https://forum.networklessons.com/t/bgp-backdoor-routes/1109>\
**Category:** Lessons Discussion\
**Created:** [December 26, 2016, 10:58pm UTC](https://forum.networklessons.com/t/bgp-backdoor-routes/1109 "2016-12-26T22:58:40Z")\
**Posts on this page:** 1\
**Showing post:** 26

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**Author:** ![lagapidis](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/lagapidis/32/4949_2.png) [@lagapidis](https://forum.networklessons.com/u/lagapidis)\
**Post date:** [August 16, 2026, 4:41am UTC](https://forum.networklessons.com/t/bgp-backdoor-routes/1109/26 "2026-08-16T04:41:54Z")

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Hello David

I think most of your questions here have been answered in this post here:

> [@MPLS Layer 3 VPN Explained](https://forum.networklessons.com/t/mpls-layer-3-vpn-explained/1287/233):
>
> Hello David allowas-in and as-override are not loop-prevention mechanisms. On the contrary, they disable BGP’s AS-path loop check so that the prefix can be accepted, and your feeling that these seemingly necessary commands can cause problems is correct. Now, whether the MPLS path then gets preferred over the local OSPF path depends on BGP best-path tie-breaking. By default, such a setup is “safe” from loops because of BGP’s default behavior. However, this “safety” is, at best, fragile in a …

> [@davidilles](#):
>
> There feels like a lot that goes into this and different design will create different considerations, so I just wanted to share my thoughts here.

Yes that is indeed the case. I think the most important thing here is that it is best practice to implement SoO regardless of whether or not you “need” it. You would never want to route traffic to the ISP that should be routed internally, so by implementing SoO you are safeguarding this behavior.

> [@davidilles](#):
>
> For example, in terms of suboptimal routing, R3 does receive the route back but **doesn’t prefer it**. This makes sense because it’s also originating that route with a very high weight.

Of course, that makes sense, but even having that unpreferred route being received can be problematic. If at some point in the future you change the weight or another configuration to influence traffic differently, you may inadvertently cause a loop or suboptimal routing, requiring you to troubleshoot until you find the culprit. By implementing SoO initially, you safeguard the correct behaivior regardless of what other configs you may apply.

I hope this has been helpful!

Laz

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