[quagga-users 14639] Re: BGP MED question (using quagga-1.2.0)

A few thought on this:

1) Metric <> MED. They are different values set different ways.
2) MEDs are inherently broken (inherently, not specifically in Quagga). Because of this they get a lot less use than you might think. A bit of googling can probably satisfy any desire for details you may have.
3) I would guess (without any proof, but with pretty good confidence) that the commands you're using are not well-tested code paths in Quagga. That means a higher risk of bugs biting you.

Maybe if you tell us more about what you're doing, someone will suggest a better way.

/a

On Mar 8, 2017, at 7:11 PM, Templin, Fred L <[email protected]> wrote:
> I am setting up a little IPv6 BGP test network using quagga-1.2.0 with three BGP
> routers; each in its own AS. Router R1 is in AS1, router R2 is in AS2 and router R3
> is in AS3. R1 peers with R2 and R3, but R2 and R3 do not peer with each other.
> All three routers are connected to the same multi-access link (for example,
> an Ethernet LAN segment). All three routers use IPv6 link-local addresses on
> their interface connections to the multi-access link (R1 is fe80::1, R2 is fe80::2
> and R3 is fe80::3).
> 
> I have configurations in routers R2 and R3 that attempt to set the MED values
> for routes originated from those routers. See below for more on that.
> 
> On R1, I have the following lines in the BGP configuration:
> 
>          bgp bestpath as-path ignore
>          bgp always-compare-med
>          bgp deterministic-med
> 
> To my understanding, the first line tells BGP to ignore the AS_PATH rule in
> the BGP route selection process. The second line tells BGP to compare the
> MED values even if the same IPv6 route is originated from different ASes.
> And, the third line I added for good measure even though I'm not sure I
> fully understand its use. Do these configurations look correct?
> 
> On R2, I set the MED value to 10000 and on R3 I set the MED value to 5000.
> But, when I install the same IPv6 route on both R2 and R3 (e.g., 2001::/64)
> R1 shows R2 as being the best next hop. But, because of the MED settings,
> I was expecting R3 to be selected.
> 
> As a clue, when I open a vtysh on R1 I get the following:
> 
> ------------------------------------------------
> r1# sh ipv6 bgp
> BGP table version is 0, local router ID is 10.0.1.2
> Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
>              r RIB-failure, S Stale, R Removed
> Origin codes: i - IGP, e - EGP, ? - incomplete
> 
>   Network          Next Hop            Metric LocPrf Weight Path
> *  2001::/64        fe80::3               1024             0 3 ?
> *>                  fe80::2               1024             0 2 ?
> 
> Total number of prefixes 1
> ---------------------------------------------------
> 
> So the routing table shows the 2001::/64 route coming from both R2 and R3,
> but both have Metric set to 1024 and the route from R2 shows up as the
> preferred route. I was rather expecting to see the Metric for R2 as 10000
> and the Metric for R3 as 5000. So, this makes me wonder if I haven't set
> the Metrics correctly in my R2/R3 config files. See below for the config
> file entries for router R2. Router R3 has very similar entries so I will not
> send its config for now. And, if you need to see more of the router R1
> configuration I could send that too.
> 
> Thanks in advance for your thoughts on this,
> 
> Fred Templin
> [email protected]
> 
> Router R2 configs:
> *************
>        interface eth0
>          ip address 10.0.0.2/24
>        !
>        interface aero0
>          ipv6 address fe80::2/64
>        !
>        !
>        ! BGP configuration
>        !
>        ! You should configure the AS number below,
>        ! along with this router's peers.
>        !
>        router bgp 2
>          bgp router-id 10.0.0.2
>          no bgp default ipv4-unicast
>          neighbor fe80::1 remote-as 1
>          neighbor fe80::1 interface aero0
>          neighbor fe80::1 advertisement-interval 0
>          neighbor fe80::1 route-map setmetricout out
>          address-family ipv6
>          redistribute connected
>          redistribute static
>          redistribute kernel
>          neighbor fe80::1 activate
>          neighbor fe80::1 next-hop-self
>          neighbor fe80::1 distribute-list 101 out
>          exit-address-family
>          !
>          ipv6 access-list 101 permit 2001::/16
>          ipv6 access-list 101 deny any
>          route-map setmetricout permit 10
>                set metric 10000
>          !