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show interface tunnels MTU question

I got this question from a co-worker and I don't have a good explaination for it.

When looking at "Show itnerface tunnel #" what/where does the first MTU refer to (in red) and where does it pull that default from? On physical interfaces it is the physical MTU, on tunnels generally I pay attention to the tunnel MTU (in blue), but we noticed the first MTU in red ... nothing is manually set on our side, brand new devices out of box connecting to a telco managed router, and that is a rather large number. Any ideas?

Tunnel3 is up, line protocol is up

  Hardware is Tunnel

  Description:

  Internet address is 10.200.70.1/24

  MTU 17900 bytes, BW 100 Kbit/sec, DLY 50000 usec,

    reliability 255/255, txload 255/255, rxload 255/255

  Encapsulation TUNNEL, loopback not set

  Keepalive set (3 sec), retries 3

  Tunnel source 192.168.255.249 (Vlan201), destination 192.168.254.2

  Tunnel Subblocks:

      src-track:

        Tunnel3 source tracking subblock associated with Vlan201

          Set of tunnels with source Vlan201, 3 members (includes iterators), on interface <OK>

  Tunnel protocol/transport GRE/IP

    Key disabled, sequencing disabled

    Checksumming of packets disabled

  Tunnel TTL 255, Fast tunneling enabled

  Tunnel transport MTU 1476 bytes

Tunnel3 is up, line protocol is up

  Hardware is Tunnel

  Description: MPLS connection to Carolina

  Internet address is 10.200.70.1/24

  MTU 17900 bytes, BW 100 Kbit/sec, DLY 50000 usec,

    reliability 255/255, txload 255/255, rxload 255/255

  Encapsulation TUNNEL, loopback not set

  Keepalive set (3 sec), retries 3

  Tunnel source 192.168.255.249 (Vlan201), destination 192.168.254.2

  Tunnel Subblocks:

      src-track:

        Tunnel3 source tracking subblock associated with Vlan201

          Set of tunnels with source Vlan201, 3 members (includes iterators), on interface <OK>

  Tunnel protocol/transport GRE/IP

    Key disabled, sequencing disabled

    Checksumming of packets disabled

  Tunnel TTL 255, Fast tunneling enabled

  Tunnel transport MTU 1476 bytes

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Rising star

show interface tunnels MTU question

3 REPLIES 3
Rising star

show interface tunnels MTU question

Beginner

Re: show interface tunnels MTU question

Hello everyone,
I have this problem too.
Please somebody have the explaination of this two value of MTU?

Thanks!!
Engager

Re: show interface tunnels MTU question

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