The MPLS WG Archive

[Roger Pottier <roger_pottier@yahoo.com>]

Hi,

 

 If i have "send label" configured for a BGP peer, do the peers need to be on directly

connected interfaces? If it is not, how would the MPLS switches in between know

about the labels?

And if it is on directly connected interfaces, does it allocate a label from  the interface label spaceof that interface?

 

 I guess, for carrier's Carrier case, the CEs need to be on directly connected interfaces with the PE.

 

Thanks,

Roger.

Marc Binderberger <marc@sniff.de> wrote:

Hi Roger,

> As you said, this could have some scaling limitations. Does LDP assign
> a label to each route learnt by the IGP. I think, LDP does not assign
> labels for BGP Learnt routes. Can cisco be configured to send labels
> for some BGP Learnt routes?


From a test setup. The box is a 7507 w/ 12.0(25)S1:

router bgp 65017
bgp router-id 192.168.249.250
bgp cluster-id 3239121353
bgp log-neighbor-changes
bgp deterministic-med
bgp bestpath compare-routerid
neighbor 192.168.249.17 remote-as 65018
neighbor 192.168.249.17 password 7 070D2D4D460B151015100E1E4A6465
!
address-family ipv4
redistribute isis TEST level-2 route-map ISIS-TO-BGP
neighbor 192.168.249.17 activate
neighbor 192.168.249.17 send-label
no auto-summary
no synchronization
exit-address-family


R1-7507#show ip bgpBGP table version is 4, local router ID is 192.168.249.250
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path
*> 192.168.249.251/32
192.168.249.46 10 32768 ?
*> 192.168.17.206/32
192.168.249.17 10 0 65018 ?

R1-7507#show ip bgp 192.168.17.206/32
BGP routing table entry for 192.168.17.206/32, version 4
Paths: (1 available, best #1)
Not advertised to any peer
65018
192.168.249.17 from 192.168.249.17 (192.168.249.241)
Origin incomplete, metric 10, localpref 100, valid, external,
best,
mpls labels in/out 106/18


So R1 receives label "18" via eBGP, the LDP binds local label "106".
This happens even without a redistribution into the IGP.

On router "R3" (belonging to AS65017):

R3-7204#show mpls ldp bindings 192.168.17.206 32 detail
tib entry: 192.168.17.206/3! 2, rev 37
local binding: tag: 203
Advertised to:
192.168.249.250:0
remote binding: tsr: 192.168.249.250:0, tag: 106


BTW, with 12.2(18)S it did not work.



>> Using iBGP IPv4+label - haven't tested yet as no IOS for 7600 (our PE
>> plattform) was available supporting this. As I understand the theory
>> this results in a packet with 3 labels minimum: the MP-BGP VPN label
>> at
>> the bottom, then the IPv4 next hop label and topmost the LDP label to
>> the ASBR.
>
> The IPv4 Nexthop Label (Middle one) would be assigned by the ASBR?

Yes. But let me try to get 1-2 more test boxes in the setup. Seeing is
believing :-)


Regards, Marc
--
Marc Binderberger Powered by *BSD ;-)

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