Following the labels
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This post is related to the following IOS Message, that got my attention while preparing to Study MPLS TE %BGP-4-VPNV4NH_IF: Nexthop 192.168.89.8 may not be reachab le from neigbor 192.168.79.7 – not a loopback |
Initial Configurations
router bgp 789 no synchronization bgp log-neighbor-changes neighbor 7.7.7.7 remote-as 789 neighbor 7.7.7.7 shutdown neighbor 7.7.7.7 update-source Loopback0 neighbor 192.168.79.7 remote-as 789 neighbor 192.168.79.7 update-source Serial0/0/0.89 no auto-summary ! address-family vpnv4 neighbor 7.7.7.7 activate neighbor 7.7.7.7 send-community extended neighbor 192.168.79.7 activate neighbor 192.168.79.7 send-community extended exit-address-family ! address-family ipv4 vrf AS56 redistribute ospf 1 vrf AS56 match internal external 1 external 2 no synchronization network 8.8.8.8 mask 255.255.255.255 exit-address-family
We can tell from the output that I am pering with R7 interface connected to R9 from R8, the same holds true for the
R7, R8 peering, using interface connecting R8 – R9
R8#show ip bgp vpnv4 all summ | b Neigh Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 7.7.7.7 4 789 8 8 0 0 0 00:01:14 Idle (Admin) 192.168.79.7 4 789 8 8 55 0 0 00:01:03 3
Now in R7
R7#show ip bgp vpnv4 rd 8.8.8.8:68 BGP table version is 54, local router ID is 7.7.7.7 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete</pre> <pre>Network Next Hop Metric LocPrf Weight Path Route Distinguisher: 8.8.8.8:68 *i6.6.6.6/32 192.168.89.8 65 100 0 ? *i8.8.8.8/32 192.168.89.8 0 100 0 i *i192.168.68.0 192.168.89.8 0 100 0 ?
and one Client that is haging over VRF AS56
R5#show ip route ospf 6.0.0.0/32 is subnetted, 1 subnets O IA 6.6.6.6 [110/129] via 192.168.57.7, 00:00:00, Serial0/0/0.57 8.0.0.0/32 is subnetted, 1 subnets O E2 8.8.8.8 [110/1] via 192.168.57.7, 00:00:00, Serial0/0/0.57 O IA 192.168.68.0/24 [110/65] via 192.168.57.7, 00:00:00, Serial0/0/0.57
Notice that those routes are INTER Area OSPF Learned routes, we can conclude that the sham link is not operating
corretly.
R5#show ip route 6.6.6.6 Routing entry for 6.6.6.6/32 Known via “ospf 1″, distance 110, metric 129, type inter area Last update from 192.168.57.7 on Serial0/0/0.57, 00:04:30 ago Routing Descriptor Blocks: * 192.168.57.7, from 192.168.57.7, 00:04:30 ago, via Serial0/0/0.57 Route metric is 129, traffic share count is 1</pre>
R5 should see this route as INTRAArea, because of a Sham Link configuration between R7 and R8, we
can tell here, that we have a Problem inside the ISP BB, remember I have R7 and R8 peering to each other using
the interfaces that they connect to R9, in order to force a pop at R9 to R7 or viceversas. looking at the problem in
more detail view at the LSP between R7 and R8 , R7 is receiving this labels from R8 to be used as the VPNV4 label.
R7#show ip bgp vpnv4 rd 8.8.8.8:68 labels Network Next Hop In label/Out label Route Distinguisher: 8.8.8.8:68 6.6.6.6/32 192.168.89.8 nolabel/20 8.8.8.8/32 192.168.89.8 nolabel/21 192.168.68.0 192.168.89.8 nolabel/19
now R7, must perform a lookup to reach 6.6.6.6 next hop, which is found in the global routing table using label:
R7(config)#do show ip cef 192.168.89.8 192.168.89.0/24, version 46, epoch 0, cached adjacency to Serial0/0/0.79 0 packets, 0 bytes tag information set, shared local tag: 16 via 192.168.79.9;, Serial0/0/0.79, 3 dependencies next hop 192.168.79.9, Serial0/0/0.79 valid cached adjacency
POP, COOL!!!
192.168.89.8 which is the next hop, R7 is receiving POP from R9, looking at the LIB
R7(config)#do show mpls ldp bind <strong>192.168.89.0 24 tib entry: 192.168.89.0/24, rev 8 local binding: tag: 16 remote binding: tsr: 9.9.9.9:0, tag: imp-null
and looking the same information at the LFIB
R7#show mpls forwarding-table 192.168.89.0 Local Outgoing Prefix Bytes tag Outgoing Next Hop tag tag or VC or Tunnel Id switched interface 16 Pop tag 192.168.89.0/24 0 Se0/0/0.79 point2point
The same shows in R9 now.
R9#show mpls ldp bin 192.168.89.0 24 tib entry: 192.168.89.0/24, rev 2 local binding: tag: imp-null remote binding: tsr: 8.8.8.8:0, tag: imp-null remote binding: tsr: 7.7.7.7:0, tag: 16
Let change the now, the BGP peering, from R7 and R8 but now using the loopbacks to establish the peering.
R7(config)#router bgp 789 R7(config-router)#neigh 192.168.89.8 sh %BGP-5-ADJCHANGE: neighbor 192.168.89.8 Down Admin. shutdown R7(config-router)# R7(config-router)#no neigh 8.8.8.8 sh
The same for R8
R8#show ip bgp summ BGP router identifier 8.8.8.8, local AS number 789 BGP table version is 1, main routing table version Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 7.7.7.7 4 789 8 8 0 0 0 00:21:04 Idle (Admin) 192.168.79.7 4 789 27 27 0 0 0 00:00:14 Active R8#conf ter Enter configuration commands, one per line. End with CNTL/Z. R8(config)#router bgp 789 R8(config-router)#no neigh 7.7.7.7 sh R8(config-router)# %BGP-5-ADJCHANGE: neighbor 7.7.7.7 Up R8(config-router)# R8(config-router)# neigh 192.168.79.7 sh
Now the BGP Peering came up from each PE router using now the loopbacks
R8(config)#do show ip bgp summ BGP router identifier 8.8.8.8, local AS number 789 BGP table version is 1, main routing table version 1</pre> Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 7.7.7.7 4 789 15 15 1 0 0 00:00:14 0 192.168.79.7 4 789 27 27 0 0 0 00:00:35 Idle (Admin)
And I got this a few seconds later the BGP between PE Router came up
%OSPF-5-ADJCHG: Process 1, Nbr 192.168.57.7 on OSPF_SL0 from LOADING to FULL, Loading Done
We can see also that the Sham Link Went UP as well 
So it seems like a good indication
that we are now configuring MPLS VPN correctly for this particular case.
– Quick show ip route in R5
R5#show ip route ospf
6.0.0.0/32 is subnetted, 1 subnets
O 6.6.6.6 [110/130] via 192.168.57.7, 00:07:33, Serial0/0/0.577.0.0.0/32 is subnetted,
1 subnets
O E2 7.7.7.7 [110/1] via 192.168.57.7, 00:07:33, Serial0/0/0.57
8.0.0.0/32 is subnetted, 1 subnets
O E2 8.8.8.8 [110/1] via 192.168.57.7, 00:07:33, Serial0/0/0.57
O 192.168.68.0/24 [110/129] via 192.168.57.7, 00:07:33, Serial0/0/0.57
R5#
You can see that now the routes are intra area routes. Let see how this different commands can be used to know thelabels are now used, in the LSP to reach the R6 lo0 from R7 at the VRF
R7#show mpls for vrf AS56 6.6.6.6 Local Outgoing Prefix Bytes tag Outgoing Next Hop tag tag or VC or Tunnel Id switched interface None 18 6.6.6.6/32 0 Se0/0/0.79 point2point
the VPN Label learn from R8
R7#show ip bgp vpnv4 rd 8.8.8.8:68 labels Network Next Hop In label/Out label Route Distinguisher: 8.8.8.8:68 6.6.6.6/32 8.8.8.8 nolabel/20 8.8.8.8/32 8.8.8.8 nolabel/21 192.168.68.0 8.8.8.8 nolabel/19
Now R7 to reach the Next hop is going to impose label 20 going out to destination 6.6.6.6 but to reach the next hop( 8.8.8.8 ) he is
R7#show mpls forwarding-table 8.8.8.8 32 Local Outgoing Prefix Bytes tag Outgoing Next Hop tag tag or VC or Tunnel Id switched interface 17 18 8.8.8.8/32 0 Se0/0/0.79 point2point
going to use label 18. Lets do a Traceroute from R5 which is acting as a Client VRF to R6, that isconnected to the VRF that is importing R5 Route Targets inside the VRF,
R7#traceroute vrf AS56 6.6.6.6 so lo756 Type escape sequence to abort. Tracing the route to 6.6.6.6</pre> <pre>1 192.168.79.9 [MPLS: Labels 18/20 Exp 0] 168 msec 200 msec 200 msec 2 192.168.68.8 [MPLS: Label 20 Exp 0] 228 msec 60 msec 60 msec 3 192.168.68.6 44 msec * 44 msec
Now R9
R9#show mpls forwarding-table 8.8.8.8 Local Outgoing Prefix Bytes tag Outgoing Next Hop tag tag or VC or Tunnel Id switched interface 18 Pop tag 8.8.8.8/32 3506 Se0/0/0.89 point2point
if a label packet comes with 18 it should POP the packet and send it to Se0/0/0.89 where R8 is, now R8 is going tosee the following label arricing arriving as MPLS: Label 20 Exp 0
MPLS: Se0/0/0.89: recvd: CoS=0, TTL=253, Label(s)=20 MPLS: Se0/0/0.68: xmit: (no label)</pre> R8#show mpls forwarding-table labels 20 Local Outgoing Prefix Bytes tag Outgoing Next Hop tag tag or VC or Tunnel Id switched interface 20 Untagged 6.6.6.6/32[V] 40032 Se0/0/0.68 point2point
He is sending the packet as Normal IP Packet to R6, and then normal IP Destination based routing is perform on R6,since we just have basic Routing configured there.
R8#show ip vrf interfaces Interface IP-Address VRF Protocol Se0/0/0.68 192.168.68.8 AS56 up Lo856 8.8.8.8 AS56 up
MPLS VPNS, cool thing!!
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