[j-nsp] MTU on RSVP tunnel

[Harry Reynolds]

Are you pinging with DNF set?

Could be ingress node is seeing Ip and trying to frag based on the
smaller inet mtu. Does seem frag would be based on packet's egress
next-hop, which is mpls in this case, but not sure we do that at
ingress.


HTHs


 

-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net
[mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Eric Van Tol
Sent: Monday, October 27, 2008 7:14 AM
To: juniper-nsp at puck.nether.net
Subject: [j-nsp] MTU on RSVP tunnel

Hi all,
It's been a long time since I've done anything with MPLS and tunnels in
general, so I need the braintrust that is juniper-nsp to verify my
thoughts on something.  I have a simple three router network as such:

R1--R2--R3

MPLS is configured on all core interfaces and an RSVP tunnel exists
between R2 and R3 (and vice versa).  Customer routes are configured to
export to BGP, so almost all routes on both R1 and R3 are seen as best
path through the tunnel.  Ethernet MTU on the core interfaces is set to
9192, with MPLS MTU set to 1548, and IP MTU set to 1500.  I can't send
anything through the tunnel larger than 1468-bytes.

Seeing's how my MTU settings on all core interfaces should leave plenty
of unnecessary headroom, would I be correct in my presumption that the
underlying circuit buildout from the carrier may not allow a physical
media MTU over 1500?  There's a few reasons I came to this conclusion,
but would like to know if I'm missing anything blatantly obvious in my
configs:

R1:
interfaces {
    ge-0/0/0 {
        mtu 9192;
        unit 0 {
            family inet {
                mtu 1500;
                address x.x.224.2/30;
            }
            family mpls {
                mtu 1548;
            }
        }
    }
}
protocols {
    rsvp {
        interface ge-0/0/0.0;
    }
    mpls {
        path-mtu {
            rsvp mtu-signaling;
        }
        label-switched-path to_r3 {
            to x.x.207.3;
            no-decrement-ttl;
        }
        interface ge-0/0/0.0;
    }
}

R2:
interfaces {
    ge-0/3/2 {
        mtu 9192;
        unit 0 {
            family inet {
                mtu 1500;
                address x.x.224.1/30;
            }
            family mpls {
                mtu 1548;
            }
        }
    }
    ge-0/3/3 {
        vlan-tagging;
        mtu 9192;
        unit 0 {
            vlan-id 1;
            family inet {
                mtu 1500;
                address x.x.224.5/30;
            }
            family mpls {
                mtu 1548;
            }
        }
    }
}
protocols {
    rsvp {
        interface ge-0/3/2.0;
        interface ge-0/3/3.0;
    }
    mpls {
        interface ge-0/3/3.0;
        interface ge-0/3/2.0;
    }
}

R3:
interfaces {
    ge-0/0/0 {
        vlan-tagging;
        mtu 9192;
        unit 0 {
            vlan-id 1;
            family inet {
                mtu 1500;
                address x.x.224.6/30;
            }
            family mpls {
                mtu 1548;
            }
        }
    }
}
protocols {
    rsvp {
        interface ge-0/0/0.0;
    }
    mpls {
        path-mtu {
            rsvp mtu-signaling;
        }
        label-switched-path to_r2 {
            to x.x.207.2;
            no-decrement-ttl;
        }
        interface ge-0/0/0.0;
    }
}

Thanks,
evt

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