Routing

Dear Community members,

I'm looking for a way to treat specific ISIS prefixes with a higher priority than other. I would like to tag them with a high priority tag.

In Cisco IOS you configure the tagging of local prefixes under the specific interface, and you instruct the isis process to give high or medium priority to specific tag.

Router(config)# int lo 0

Router(config-if)# isis tag 100

Router(config)#router isis

Router(config-router)# ip route priority high tag 100

Router(config-router)# ip route priority medium tag 200

I'm trying to accomplish the same thing in JUNOS and I believe that this can be done via a policy-option statement and then the application of the policy under the protocol isis hierarchy.

[edit policy-options policy-statement ISIS-HIGH-PRIORITY]

dele@test-mx00# show

term 1 {

    from {

        protocol isis;

        tag 100;

    }

    then priority high;

}

term 2 {

    from {

        protocol direct;

        route-filter 10.10.10.1/32 exact; (this is Lo0 IP address)

    }

    then {

        tag 100;

        priority high;

    }

}

[edit protocols isis]

dele@test-mx00# show

export ISIS-HIGH-PRIORITY;

I would like to kindly ask you for a verification. I can see the tag set on the neighbor MX router.

dele@test-mx01# run show route 10.10.10.1              

inet.0: 11876 destinations, 11972 routes (11875 active, 0 holddown, 1 hidden)

Restart Complete

+ = Active Route, - = Last Active, * = Both

10.10.10.1/32      *[IS-IS/18] 00:33:22, metric 10, tag 100

                    > to 192.168.10.1 via xe-0/0/0.0

                      to 192.168.10.5 via xe-0/0/1.0

Has ISIS in JunOS the ability to treat prefixes with a higher priority than other?  How can I verify that this prefix will be treated via ISIS with higher priority than other non-tagged prefixes? The policy-statement is correct?

Best Regards

Dimitris

Hi Dimitris:

Obviously it won't work. The action "priority" wil only work for OSPF import policy. You may try "preference" action instead. In JUNOS world, "preference" is the value which equals to CISCO's "admin distance".

Conty

Hello Conty,

thanks for your reply.I was afraid that only OSPF can tag high priority prefixes and also treat them accordingly

Correct me if I'm wrong but preference for JunOS does what the Cisco admin distance and differentiate the priority among protocols and for routes/prefixes learned via many routing protocols, it will choose the one with the lowest preference.

Hence, for ISIS I cannot tag some of the prefixes learned with high priority, in order to place them first in the RIB, in case of a protocol reconvergence.

Any reply will be highly appreciated

BR/Dimitris

Hi,

AFAIK there is no such mechanism for ISIS (I just double-checked at http://www.juniper.net/techpubs/en_US/junos10.4/topics/usage-guidelines/policy-configuring-actions-in-routing-policy-terms.html😞 Priority only seems to work for OSPF, preference is something else and ... That's it unfortunately.

But as I'm for sure not an authority on this, let's see what the real geniuses come up with.

Best Regards

Ulf

ISIS doesn't support this feature.

Can anybody make my doubt clear on the discussion regarding OSPF import policy that is being discussed here.

Can we apply some ospf import policy and change prefrence or priority...???

Awaiting expert opinion...

if you want selected prefixs has higher preference through ISIS than static and ospf, use this policy to control them.

set protocol isis export preference-prefix-by-isis;

set policy-options policy-statement preference-prefix-by-isis term 5 from prefix-list aaa;

set policy-options policy-statement preference-prefix-by-isis term 5 then accept preference subtract 14;

Due to static route preference is 5; ospf preference is 10; isis level 1 is 15, and isis level 2 is 18, here has deduction of 14, so the selected prefix through ISIS has higher preference 1 (level 1) and 4 (level 2) than ospf and static routes.

Cheers,
Sam