Routing

So we have run into an interesting problem trying to do unnumbered OSPF between our MX routers and our EX switches.

We are running into an issue where we get the following on the EX:

OSPF packet ignored: netmask 255.255.255.255 mismatch from 10.10.10.10 on intf ae0.100 area 0.0.0.0

We then get this on the MX side:

OSPF packet ignored: netmask 0.0.0.0 mismatch from 10.10.10.11 on intf ae0.100 area 0.0.0.0

I'm not sure what the resolution would be here. We are running this just fine in other parts of our infrastructure and I'm not sure if there's a problem based on versions as we are running the 15.1 code base on the MX and the 17.2 code base on the EX series.

Seems odd that the unnumbered OSPF subnet mask for a /32 would be different between the two versions.

Here's the sanatized configuration of our MX side, the EX side looks identical.

mx# show interfaces ae0
vlan-tagging;
aggregated-ether-options {
    minimum-links 1;
    link-speed 10g;
    lacp {
        active;
        periodic fast;
    }
}
unit 100 {
    vlan-id 100;
    family inet {
         unnumbered-address lo0.100;
    }
}

mx# show interfaces lo0.100
family inet {
    address 10.10.10.10/32;
}

mx# show protocols ospf area 0.0.0.0
interface ae0.100 {
    interface-type p2p;
}

any input or information would be extremely helpful here!

Thanks

Do you have the lo0 interface also assigned to ospf area 0 as a passive interace?

Yes, EX has the same configuration as well:

mx# show protocols ospf area 0.0.0.0
interface lo0.100 {
    passive;
}

Here's the full OSPF trace as well:

Dec 13 02:22:47.778079 OSPF rcvd Hello 10.10.10.10 -> 224.0.0.5 (ae1.100 IFL 344 area 0.0.0.0)
Dec 13 02:22:47.778082   Version 2, length 44, ID 10.10.10.10, area 0.0.0.0
Dec 13 02:22:47.778084   checksum 0x0, authtype 2
Dec 13 02:22:47.778086   mask 255.255.255.255, hello_ivl 10, opts 0x12, prio 128
Dec 13 02:22:47.778088   dead_ivl 40, DR 0.0.0.0, BDR 0.0.0.0
Dec 13 02:22:47.778090 OSPF restart signaling: Received hello with LLS data from nbr ip=10.10.10.10 id=10.10.10.10.
Dec 13 02:22:47.778092 OSPF packet ignored: netmask 255.255.255.255 mismatch from 10.10.10.10 on intf ae1.100 area 0.0.0.0

Hi nertwork,

This is a difference in behavior between versions for which there's a hidden knob "backward-compatible-unnumbered-mask" added in newer versions: https://prsearch.juniper.net/InfoCenter/index?page=prcontent&id=PR1374525

set protocols ospf area 0.0.0.0 interface ae.0 interface-type p2p
set protocols ospf area 0.0.0.0 interface ae.0 backward-compatible-unnumbered-mask

Also, there's one more problem that doesn't let this to work on 17.3R3-S1 but fixed on 17.3R3-S2.  So its best to one the 18.x recommended versions depending on which EX you're using: https://kb.juniper.net/InfoCenter/index?page=content&id=KB21476&actp=METADATA

Just for the sake of completeness, here's the 17.3 issue fix:

https://prsearch.juniper.net/InfoCenter/index?page=prcontent&id=PR1386891

Hope this helps.

Regards,
-r.

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