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Not So Fast Ansible, Cisco IOS Can’t Keep Up…

Remember how earlier releases of Nexus-OS started dropping configuration commands if you were typing them too quickly (and how it was declared a feature ;)?

Mark Fergusson had a similar experience on Cisco IOS. All he wanted to do was to use Ansible to configure a VRF, an interface in the VRF, and OSPF routing process on Cisco CSR 1000v running software release 15.5(3).

Here’s what he was trying to deploy. Looks like a configuration straight out of an MPLS book, right?

ip vrf Customer_A
 rd 65000:1
 route-target import 65000:1
 route-target export 65000:1
!
interface GigabitEthernet1.146
 ip vrf forwarding Customer_A
 ip address 155.1.146.1 255.255.255.0
 ip ospf 2 area 0

router ospf 2 vrf Customer_A
  router-id 155.1.146.1
  redistribute bgp 65000 subnets

Guess what… when he tried to push that configuration to his CSR 1000v with Ansible ios_config module the in-VRF OSPF router process refused to start claiming it cannot get a router ID (%OSPF-4-NORTRID: OSPF process 2 failed to allocate unique router-id and cannot start). The whole thing worked when he tried to configure OSPF a bit later – looks like it takes some time to get a subinterface ready after it’s been configured, and if you’re typing too quickly you’re out of luck.

Keep in mind that Ansible uses SSH session to configure a Cisco IOS device, so it’s doing the exact same thing as if you’d be a really fast typist.

I could see two immediate solutions to this problem:

  • Get a router that has a decent API and all-or-nothing commit mechanism;
  • Split the configuration in two parts and push them to the device using two ios_config calls. It takes Ansible long enough to work through its gazillion layers of abstraction for Cisco IOS to realize what just happened.

On a somewhat tangential note, a friend of mine called the current state of network automation “Unix Scripting in 1970s”. Unfortunately he wasn’t too far off…


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3 comments:

  1. On a somewhat tangential note, a friend of mine called the current state of network automation “Unix Scripting in 1970s”.

    Sure - except that instead of config files, you have to manually run all of the commands that init and RC scripts do when you first install, and when you type "write mem" it just copies your bash history file to rc.local for the next time you reboot.

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  2. I think there should be a 'type slowly'/'paste slowly' variable for just this reason.

    I ran into this before Palo Alto released a community plugin for configuring anything (previously only certain, specific things could be configured with the PAN ansible module) I was using the ios module to try and configure PAN through the CLI. I ran into the same issue above - lines would get missed.


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  3. You are a really fast typist OR you have prepared a configuration ahead of time (possibly in a lab) which you are now pasting in.

    Copy and pasting valid sections of config ought to work without issues.
    I think the only way to describe the IOS behavior in that case is: seriously annoying bug that can cause unexpected problems for people configuring equipment.

    There should not be race conditions like that between entering parts of a configuration and the configs becoming active --- they could buffer the remaining config lines until the subinterface is at least created
    and ready to be the subject of more config lines.

    ReplyDelete

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