[FROG] Routes learned from iBGP are not maintaining Metrics when advertised to eBGP peers

[Lou Berger]

My memory is we don't send the med to eBGP peers... See 
https://tools.ietf.org/html/rfc4451#section-3.1

Lou


----------
On October 23, 2019 8:31:52 AM Lee Clements <lclements0 at gmail.com> wrote:

> Doing some testing on FRR here, and hoping for some assistance.  Hopefully
> this is the right place to go.  If not, please let me know!
>
> I've got 3 remote iBGP peers that are configured as standard iBGP peers.
> These two iBGP peers learn some routes locally and then re-advertise these
> prefixes over a full-mesh iBGP network to each other, with FRR being one of
> the four routers in the mesh.  The other three iBGP peers are Cisco.
>
> FRR has one eBGP peer, to replicate re-advertising these routes out to
> iBGP.  In our other three iBGP peers, we leverage route-maps to increment
> the received MED value of the route, so that we can prefer locally received
> eBGP routes - all else being equal - as opposed to those learned from our
> iBGP speakers in other locations.  We also do this so locally originated
> prefixes from our AS have a higher metric when going out to eBGP speakers
> so they don't inadvertently get preferenced when there's a better path for
> the route to take.
>
> I am receiving the routes from our iBGP speakers fine, and see the
> incremented MED on receipt of the routes from the aforementioned speaker.
> When I configure a local (to FRR) iBGP speaker as a route-reflector-client
> within the same AS, these pre-incremented MED's are correctly advertised to
> the local iBGP speaker and work just fine.
>
> When advertising these same prefixes to an eBGP speaker with a different
> AS, the metric's are not readvertised, and only a locally originated prefix
> maintains any sort of metric at all.
>
> Route's received from one of our remote iBGP speakers:
>
> routert# sh bgp ipv4 unicast neighbors 1.1.1.1 received-routes
> BGP table version is 0, local router ID is 2.2.2.2, vrf id 0
> Default local pref 100, local AS 1234
> Status codes:  s suppressed, d damped, h history, * valid, > best, =
> multipath,
>                i internal, r RIB-failure, S Stale, R Removed
> Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
> Origin codes:  i - IGP, e - EGP, ? - incomplete
>
>    Network          Next Hop            Metric LocPrf Weight Path
> *> 0.0.0.0/0         1.1.1.1                           100    100      0 i
> *> 1.2.3.0/20       1.1.1.1                           100    100      0 i
> *> 2.3.4.0/21       1.1.1.1                           100    100      0
> 5678 i
> *> 3.4.5.0/24       1.1.1.1                           100    100      0
> 5678 i
> *> 5.6.7.0/22       1.1.1.1                           102    100      0
> 5678 i
> *> 7.8.9.0/24       1.1.1.1                           102    100      0
> 5678 i
>
> Total number of prefixes 6
>
> Route's being correctly re-advertised and maintaining metric on
> re-advertisement to our local iBGP speaker (route-reflector-client):
>
> router# sh bgp ipv4 unicast neighbors 3.3.3.3 advertised-routes
> BGP table version is 4560509, local router ID is 2.2.2.2, vrf id 0
> Default local pref 100, local AS 1234
> Status codes:  s suppressed, d damped, h history, * valid, > best, =
> multipath,
>                i internal, r RIB-failure, S Stale, R Removed
> Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
> Origin codes:  i - IGP, e - EGP, ? - incomplete
>
>    Network          Next Hop            Metric LocPrf Weight Path
> *> 1.2.3.0/20   1.1.1.1              100    100      0 i
> *> 1.2.7.0/23   2.2.2.2              0    100  32768 i
> *> 2.3.4.0/21   1.1.1.1              100    100      0 5678i
> *> 3.4.5.0/24   1.1.1.1              100    100      0 5678 i
> *> 5.6.7.0/22   1.1.1.1              102    100      0 5678 i
> *> 7.8.9.0/24   1.1.1.1              102    100      0 5678 i
>
> Total number of prefixes 6
>
> Route's not maintaining their metric on re-advertisement to our local (to
> FRR) eBGP speaker:
>
> router# sh bgp ipv4 unicast neighbors 8.8.8.8 advertised-routes
> BGP table version is 4562244, local router ID is 2.2.2.2, vrf id 0
> Default local pref 100, local AS 1234
> Status codes:  s suppressed, d damped, h history, * valid, > best, =
> multipath,
>                i internal, r RIB-failure, S Stale, R Removed
> Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
> Origin codes:  i - IGP, e - EGP, ? - incomplete
>
>    Network          Next Hop            Metric LocPrf Weight Path
> *> 1.2.3.0/20  0.0.0.0                                   100      0 i
> *> 1.2.7.0/23  0.0.0.0                        0                  32768 i
> *> 2.3.4.0/21  0.0.0.0                                    100      0 5678i
> *> 3.4.5.0/24  0.0.0.0                                    100      0 5678 i
> *> 5.6.7.0/22  0.0.0.0                                    100      0 5678 i
> *> 7.8.9.0/24  0.0.0.0                                    100      0 5678 i
>
> Total number of prefixes 6
>
> Am I doing something wrong here?  Otherwise a pretty straight forward BGP
> setup with some basic route-maps in and out, nothing too crazy.  Is this
> expected behavior in FRR?
>
> Running latest available stable release, FRRouting 7.1RPKI.
>
> Thanks for any help.
>
>
>
> ----------
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