The Cisco and YANG models

Earlier in this chapter, we looked at the possibility of expressing the network by using the data modeling language YANG. Let's look into it a little bit more with examples.

First off, we should know that the YANG model only defines the type of data sent over the NETCONF protocol without dictating what the data should be. Secondly, it is worth pointing out that NETCONF exists as a standalone protocol, as we saw in the NX-API section. YANG, being relatively new, has a spotty supportability across vendors and product lines. For example, if we run the same capability exchange script that we have used before for a Cisco 1000v running IOS-XE, this is what we will see:

    urn:cisco:params:xml:ns:yang:cisco-virtual-service?module=cisco-
    virtual-service&revision=2015-04-09
    http://tail-f.com/ns/mibs/SNMP-NOTIFICATION-MIB/200210140000Z?
    module=SNMP-NOTIFICATION-MIB&revision=2002-10-14
    urn:ietf:params:xml:ns:yang:iana-crypt-hash?module=iana-crypt-
    hash&revision=2014-04-04&features=crypt-hash-sha-512,crypt-hash-
    sha-256,crypt-hash-md5
    urn:ietf:params:xml:ns:yang:smiv2:TUNNEL-MIB?module=TUNNEL-
    MIB&revision=2005-05-16
    urn:ietf:params:xml:ns:yang:smiv2:CISCO-IP-URPF-MIB?module=CISCO-
    IP-URPF-MIB&revision=2011-12-29
    urn:ietf:params:xml:ns:yang:smiv2:ENTITY-STATE-MIB?module=ENTITY-
    STATE-MIB&revision=2005-11-22
    urn:ietf:params:xml:ns:yang:smiv2:IANAifType-MIB?module=IANAifType-
    MIB&revision=2006-03-31
    <omitted>

Compare this to the output that we saw for NX-OS. Clearly, IOS-XE supports the YANG model features more than NX-OS. Industry-wide, network data modeling when supported, is clearly something that can be used across your devices, which is beneficial for network automation. However, given the uneven support of vendors and products, it is not yet mature enough to be used exclusively for the production network, in my opinion. For this book, I have included a script called cisco_yang_1.py that shows how to parse out the NETCONF XML output with YANG filters called urn:ietf:params:xml:ns:yang:ietf-interfaces as a starting point to see the existing tag overlay.