# AS Path Prepending on XE and XR
This short article explores what happens when you do AS path prepending and apply it outbound to an eBGP neighbor.
Consider the following topology:
R1 originates 10.10.10.10/32 into BGP. R2 uses the following route-map and applies it to the neighbor statement for R3 outbound:
```
route-map AS_PREPEND
set as-path prepend 100
!
router bgp 65001
neighbor route-map AS_PREPEND out
```
What is the AS path for 10.10.10.10/32 as seen on R3? There are two options that might make sense:
1. 100 65001 65000 i
2. 65001 100 65000 i
The answer is **65001 100 65000 i**. This is because the route-map is applied before the local AS is finally added to the AS path, when advertising the route to the eBGP peer.
```
R3#show bgp ipv4 uni | be Network
Network Next Hop Metric LocPrf Weight Path
*> 10.10.10.10/32 10.10.12.1 0 65001 100 65000 i
```
Note that this is logic is not applicable when you change the next-hop IP address in the route-map. The router doesn’t then change this to its interface address used for the eBGP session. The next-hop that the route-map sets takes precedence.
### AS Path Prepending on IOS-XR
This same logic applies when preforming AS path prepending on XR with the following route-policy:
```
#R2
route-policy AS_PREPEND
prepend as-path 100
end-policy
!
router bgp 65001
neighbor
address-family ipv4 unicast
route-policy AS_PREPEND out
```
The local AS is prepended *after* the RPL prepending takes place:
```
RP/0/0/CPU0:R3#show bgp ipv4 uni | be Network
Thu Dec 8 04:07:53.213 UTC
Network Next Hop Metric LocPrf Weight Path
*> 10.10.10.10/32 10.2.3.2 0 65001 100 65000 i
```
---
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