[ixpmanager] IXPManager: Two customers on one port

[Christopher Rössler]

Hi,

for the sflow VLAN ID on subinterfaces there is a setting that has been
introduced a while ago in EOS.
sflow extension switch vlan forwarding

here is the TOI:
https://www.arista.com/en/support/toi/eos-4-34-2f/22052-sflow-vlan-forwarding

But relabeling vlan-ids in sflow inside the sflow-to-rrd-handler is a
workaround for the meantime, as the sflowtool will use vlan-id of the
ethernet header by default and would report the wrong id as mentioned
before:

# fix for arista subinterface vlan in out and vlan translation
#
sub rewrite_subint_vlan
{
       my ($agent, $srcswport, $vlan, $ovlan) = @_;

       ###Out-VLAN will be set correctly on new switches
       return $ovlan if $ovlan == '100';

        ###relabel customer subinterface vlan-id to peering lan
        if($agent eq '<IP of switch>' && $srcswport == '<25>' && $vlan ==
'2001') {
                return '100';
        }
}
which would relabel the VLAN ID 2001 to show up as 100.


chris



On Thu, Apr 23, 2026 at 12:26 PM Nick Hilliard via ixpmanager <
ixpmanager at inex.ie> wrote:

> Salvador Bertenbreiter via ixpmanager wrote on 21/04/2026 23:57:
> > Is the subinterface method a better method to replace fanout ports? If
> > so, would that run on any HW platform (Tomahawk-based switch for
> > example), or are more advanced ASICs like Jericho required? We also use
> > mainly Arista as our IXP switches.
>
> Hi Salvador,
>
> Just on that sample configuration that Barry posted:
>
> > interface Ethernet25.2001
> >    description Cust: Resold Customer 1 Ltd
> >    encapsulation dot1q vlan 2001
> >    vlan id 10
>
> This configuration allows you to attach different incoming vlans to a
> single peering LAN, and also handles the case where ixp customer A on
> vlan 2001 wants to talk to ixp customer B on vlan 2002 on the same
> physical, but on the same LAN.  I.e. packets in and out on the same port
> - hence the "hair-pin" name.
>
> In other words, this is not the same as defining two normal
> subinterfaces with different VLAN IDs.
>
> There are limitations: the sflow vlan ID is the incoming vlan ID (i.e.
> 2001) instead of the peering lan. There are also restrictions which
> apply to layer 2 ACLs.
>
> Nick
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-- 
Christopher Rössler, Network Engineer
christopher.roessler at bcix.de
+49 30 2332195 37

BCIX Management GmbH
Albrechtstr. 110
12103 Berlin
Germany

Geschäftsführer/Managing Directors: Jens Lietzmann, André Grüneberg
Handelsregister: Amtsgericht Charlottenburg, HRB 143581 B
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