[j-nsp] MTU: old style vs new style trunk configuration on MX80

[Doug Hanks]

It's as expected; you have to use vlan-tagging to add the 4 bytes to the
MTU.  It's a documentation error.

Thank you,

-- 
Doug Hanks - JNCIE-ENT #213,  JNCIE-SP #875
Sr. Systems Engineer
Juniper Networks



On 2/9/12 4:29 PM, "Dawid Gajownik" <gajownik at gmail.com> wrote:

>Hi!
>
>I've been troubleshooting today MTU issues on my new MX80 router
>(actually MX5) with Junos 11.4R1.14. I have noticed that MTU of
>interfaces differs if I set trunks with old-style or new-style
>configuration.
>
>Documentation 
>http://www.juniper.net/techpubs/en_US/junos11.4/topics/example/layer-2-bri
>dge-domain-environment-example-interfaces-and-vlans-mx-solutions.html
>does not mention it, but with a interface-mode you have to manually
>set MTU 4 bytes larger or add "vlan-tagging" option. Is this a bug in
>Junos or documentation is incomplete? On EX4200 with interface-mode I
>did not need to add/change anything.
>
>Please take a closer look at ae1 interface:
>
>root at KR-020-r1# show ae0
>description "### KR-011-s1 ###";
>vlan-tagging;
>encapsulation extended-vlan-bridge;
>aggregated-ether-options {
>   lacp {
>       active;
>       periodic fast;
>   }
>}
>inactive: unit 0 {
>   family bridge {
>       interface-mode trunk;
>       vlan-id-list [ 708 206 ];
>   }
>}
>unit 206 {
>   vlan-id 206;
>}
>unit 708 {
>   vlan-id 708;
>}
>
>[edit interfaces]
>root at KR-020-r1# show ae1
>description "### KR-020-s1 ###";
>aggregated-ether-options {
>   lacp {
>       active;
>       periodic fast;
>   }
>}
>unit 0 {
>   family bridge {
>       interface-mode trunk;
>       vlan-id-list [ 708 206 ];
>   }
>}
>
>[edit interfaces]
>root at KR-020-r1# show ae2
>description "### KR-020-s2 ###";
>mtu 1518;
>aggregated-ether-options {
>   lacp {
>       active;
>       periodic fast;
>   }
>}
>unit 0 {
>   family bridge {
>       interface-mode trunk;
>       vlan-id-list [ 708 206 ];
>   }
>}
>
>[edit interfaces]
>root at KR-020-r1# show ae3
>description "### KR-020-s3 ###";
>vlan-tagging;
>aggregated-ether-options {
>   lacp {
>       active;
>       periodic fast;
>   }
>}
>unit 0 {
>   family bridge {
>       interface-mode trunk;
>       vlan-id-list [ 708 206 ];
>   }
>}
>
>[edit interfaces]
>root at KR-020-r1# run show interfaces ae0 | grep MTU
> Link-level type: Extended-VLAN-VPLS, MTU: 1518, Speed: 2Gbps, BPDU
>Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source
>filtering: Disabled, Flow control: Disabled,
>   Protocol bridge, MTU: 1518
>   Protocol bridge, MTU: 1518
>   Protocol multiservice, MTU: Unlimited
>
>[edit interfaces]
>root at KR-020-r1# run show interfaces ae1 | grep MTU
> Link-level type: Ethernet, MTU: 1514, Speed: Unspecified, BPDU
>Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source
>filtering: Disabled, Flow control: Disabled,
>   Protocol bridge, MTU: 1514
>
>[edit interfaces]
>root at KR-020-r1# run show interfaces ae2 | grep MTU
> Link-level type: Ethernet, MTU: 1518, Speed: 2Gbps, BPDU Error:
>None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering:
>Disabled, Flow control: Disabled,
>   Protocol bridge, MTU: 1518
>
>[edit interfaces]
>root at KR-020-r1# run show interfaces ae3 | grep MTU
> Link-level type: Ethernet, MTU: 1518, Speed: Unspecified, BPDU
>Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source
>filtering: Disabled, Flow control: Disabled,
>   Protocol bridge, MTU: 1518
>   Protocol multiservice, MTU: Unlimited
>
>[edit interfaces]
>root at KR-020-r1#
>
>Regards,
>     Dawid
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