02-03-2015 02:16 AM
Hello,
I want to test/deploy MPLS on top of our current L3 network, but i do not want our current global routing table to be label-switched (which is the default behaviour).
This should be possible if i deploy new dedicated Loopbacks for MPLS connections + do ldp label filtering on the PEs to determine what is announced inside MPLS. I tried to simulate this in a lab, but for some reason, the routers always announces ALL loopbacks. I even used "no mpls ldp advertise-labels" (which should stop all advertisements, no ?), but i still see the loopback on the next hop:
PE1
int lo0
desc Loopback for IP (OSPF)
ip add 4.4.4.1 255.255.255.255
int lo100
desc Loopback for MPLS
ip add 100.100.100.1 255.255.255.255
int Gi1/0
desc to P router
ip add 1.1.1.1 255.255.255.0
mpls ip
no mpls ldp advertise-labels
mpls ldp router-id Loopback100 force
on the P router (next hop):
P# show mpls forwarding-table
tag tag or vc prefix outgoing int next hop
20 Untagged 4.4.4.1/32 Gi1/0 1.1.1.1 <---- this one is still here, i do not want to announce 4.4.4.1, only 100.100.100.1
21 Untagged 100.100.100.1/32 Gi1/0 1.1.1.1
Could this be a bug ? running 12.4(10a) on 7200 router
regards,
Geert
02-03-2015 07:22 AM
ok, i always seem to solve my own questions :-)
Key point to remember is that local label generation is based on the local routing table, not the local interface table. Since the local routing table also contains the remote routes, a router by default also generates labels for remote routes. My filter needs to be based on the local routing table, not the local interfaces. I need to adjust my access list or prefix list matching to the following:
ip prefix-list MPLS-LO permit 100.100.100.0/24 ge 32 le 32
conf t
mpls ldp label
allocate global prefix-list MPLS-LO
only the 100.100.100.x loopbacks are announced into ldp
sh mpls forwarding
Label
21 16 100.100.100.2/32
22 Pop 100.100.100.3/32
24 19 100.100.100.1/32
<end>
On my PEs i can now use MPBGP with these next hops to run BGP on top of my existing network without affecting my existing core routing...
See also: http://www.cisco.com/c/en/us/td/docs/ios/mpls/configuration/guide/convert/mp_ldp_book/mp_ldp_alloc_filter.html
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide