Description: | Symptom:
ANrtr1 --- L2 (IOSswitch) L2 --- ANrtr2
When you connect two autonomic routers (ANrtr1, ANrtr2) via an L2 connection that is built via one or more devices providing a switched L2 connection, then AN between the two routers may fail: the autonomic control plane is not built, or if one device (e.g.: ANrtr2) is not yet AN enrolled, it will not enroll into autonomic networking.
Conditions:
This problem may happen if at least one of the device(s) terminating the L2 connection on ANrtr1 or ANrtr2 is running Cisco IOS 15.5(3)S - 15.6(1)S even though these devices are not configured for AN.
save & reload without autonomic config
Workaround:
The issues exists because of a problem on the L2 IOS device(s) between ANrtr1/ANrtr2. See further problem description below to understand the issue.
After you configure "no autonomic" on the L2 device in question, it will correctly forward CD packets between ANrtr1 and ANrtr2. The problem will reoccur after the next reboot though. To make the workaround persistent, configure an EEM script run after bootstrap:
event manager applet CSCux51388-fix-cd-forwarding
event syslog pattern "SYS-5-RESTART"
action 1.0 cli command "enable"
action 1.1 cli command "configure terminal"
action 1.2 cli command "no autonomic"
If you are running an IOS image without -k9 on the L2 device, autonomic can not be configured because it is not enabled in those images, but the problem still exists. There is no workaround for those images. You may want to change to a -k9 image in this case.
If the L2 switch is provided by a service provider incapable of enabling the above workaround, there is no full workaround possible on ANrtr1/ANrtr2: It is not possible to zero-touch enroll e.g.: ANrtr2. If both ANrtr1/ANrtr are already configured devices, you can set up the autonomic control plane between them by manually configuring a GRE tunnel between them and enabling "autonomic adjacency-discovery" on both GRE tunnel interfaces. This will not rely/use the CD protocol and therefore not be subject to this problem.
Further Problem Description:
The cause of the problem is that Cisco IOS switches/routers may not transparently forward AN CD (channel discovery) packets across the L2 connection. This inhibits the automatic AN neighbor discovery between ANrtr1 and ANrtr2. A Cisco IOS device should transparently forward these CD packets as long as AN is not enabled. The problem is that after bootstrap, the default behavior is to not-forward these packets but instead intercept them - and because AN is not enabled, they are then dropped by the device.
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