Hi all,
I'm working on IPX lab 9 and seem to be having problems with R5's handling
of bgp multipath (introduced in section 3.5).
What seems to happen is that it only assigns a label to what BGP sees as the
best-path and the cef traffic sharing ends up causing certain
souce/destination pairings to fail as a result.
R5#show ip bgp labels
Network Next Hop In label/Out label
0.0.0.0 21.1.5.21 nolabel/nolabel
100.100.100.0/24 0.0.0.0 nolabel/nolabel
100.100.100.5/32 0.0.0.0 imp-null/nolabel
100.100.100.7/32 100.100.100.7 17/imp-null
100.100.100.8/32 100.100.100.8 16/imp-null
200.200.128.0/17 100.200.45.4 nolabel/nolabel
100.200.56.6 nolabel/nolabel
200.200.200.4/32 100.200.45.4 20/imp-null
100.200.56.6 20/16
200.200.200.6/32 100.200.45.4 21/17
100.200.56.6 21/imp-null
* 200.200.200.9/32 100.200.45.4 22/16*
* 100.200.56.6 22/18*
R5#show ip cef 200.200.200.9
200.200.200.9/32, version 58, epoch 0, per-destination sharing
0 packets, 0 bytes
tag information set, all rewrites owned
local tag: 22
via 100.200.56.6, 0 dependencies, recursive
traffic share 1
next hop 100.200.56.6, Serial4/2 via 100.200.56.6/32
valid adjacency
via 100.200.45.4, 0 dependencies, recursive
traffic share 1
next hop 100.200.45.4, Serial4/3 via 100.200.45.4/32
valid adjacency
tag rewrite with Se4/3, 100.200.45.4, *tags imposed: {16}*
0 packets, 0 bytes switched through the prefix
tmstats: external 0 packets, 0 bytes
internal 0 packets, 0 bytes
In order for the LSP to work, the path via Serial 4/2 should be imposing
label 18, but it's not. The labeled path corresponds to the route BGP sees
as the bestpath:
R5#show ip bgp | be 200.200.200.9
*> 200.200.200.9/32 100.200.45.4 0 200 i
* 100.200.56.6 0 200 i
If I shut down Serial 4/3, it immediately imposes the label:
R5(config)#int se4/3
R5(config-if)#shut
R5(config-if)#
00:19:44: %BGP-5-ADJCHANGE: neighbor 100.200.45.4 Down Interface flap
R5(config-if)#
00:19:46: %LINK-5-CHANGED: Interface Serial4/3, changed state to
administratively down
00:19:47: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial4/3, changed
state to down
R5(config-if)#^Z
R5#conf t
00:20:03: %SYS-5-CONFIG_I: Configured from console by console
R5#show ip cef 200.200.200.9
200.200.200.9/32, version 62, epoch 0, cached adjacency 100.200.56.6
0 packets, 0 bytes
tag information set, all rewrites owned
local tag: 22
fast tag rewrite with Se4/2, 100.200.56.6, tags imposed: {18}
via 100.200.56.6, 0 dependencies, recursive
next hop 100.200.56.6, Serial4/2 via 100.200.56.6/32
valid cached adjacency
tag rewrite with Se4/2, 100.200.56.6, tags imposed: {18}
Everything works fine if I leave either of the links between R5 and R4/R6
shut, or if I leave multipath disabled on R5. This problem has completely
derailed my work tonight and I'd love to know if I've missed something or if
there's a workaround now that I've burned up most of my rack rental on it.
Thanks,
Eric
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