Re: L2TPv3 and the routed interface on the same router

Tod Larson · ‎10-31-2010

I have a subnet (vlan 104) working great across a WAN. At site 1, Router A (3745) has the L2TPv3 tunnel configured while Router B (7204) has a routed interface on vlan 104.

The only thing router A is doing is the tunnel, so I'd like put the tunnel on Router B and eliminate Router A.

The trouble is, when I move the configs to Router B, the tunnel comes up, but the far side does not receive traffic over the tunnel.

Router B shows sending and receiving packets (per the 'sh l2tun session all' command).

The far end router shows sending packets but receiving 0.

Is it a problem to have both the vlan 104's L2TPv3 xconnect interface and the vlan 104's routed inteface on the SAME router?

aqeel.karim · ‎11-01-2010

Question... How is the 7204 sending L2 traffic? You mentioned that the 7204 has the L3 Vlan Int... is there another interface that has the L2 traffic coming in? On the C3745, did it have the L2 traffic? I know you mentioned the C3745 had the L2TP connection point, but I"m missing the visual on the other side.

Current

L2 Switch/vl104--->C3745---(L2TPTun)-->C7204---->WAN --->Far-end Router-->(vl104/L2TPTun)-->L2 Switch/vl104

| |

---------------------------------------------------------------------------------

Change

L2 Switch/vl104--->(L2TPTun)-->C7204--->WAN --->Far-end Router-->(vl104/L2TPTun)-->L2 Switch/vl104

| |

---------------------------------------------------------------------------------

I also, wonder if there is a disconnect with your Vlan xconnect and routed interface config. I would have rather have the xconnect on the routed interface not the vlan. If you have it on the vlan but the routed interface is really the egress port how can the vlan int be the egress port too.

Which int is doing the vlan104 routing/switching? Vlan Interface or the routed interface?

Tod Larson · ‎11-01-2010

Aqeel,

The attached drawing might help clarify.

How is the 7204 sending L2 traffic? -- The output of "sh l2tun session all" says it's sending. it should be sending L2 traffic across the tunnel across the directly connected WAN interface.

You mentioned that the 7204 has the L3 Vlan Int... is there another interface that has the L2 traffic coming in? -- only the layer 3 interface and the xconnect interface.

On the C3745, did it have the L2 traffic? --only the xconnect on the 3745. The far end, a 3945, has one interface as the xconnect and another interface as the layer 3 interface.

Which int is doing the vlan104 routing/switching? Vlan Interface or the routed interface? -- the routed interface on the router. The switches are doing layer 2 only.

Thank you.

aqeel.karim · ‎11-01-2010

Tod,

A word is a word, a picture can mean a thousand (My silly analogy). If you do a trace from the L2 switch, which path does it take? Towards the router or towards the xconnect interface? When I applied this method on my routers, my switch had one way out. Pretty simple right? But in your case depending what is the default-gateway of the switch, if any is applied, your L2 traffic as two ways out. Or better yet, on the L2 switch which mac address is in the Mac table for your far-end switch?

For some reason, I think the routed interface has priority, although switchin is supposed to be faster. After you look at the mac table, do you have an option of disconnecting the routed interface on the 7204?

aqeel.karim · ‎11-01-2010

Disregard, my last about disconnected the L3 interface. You actually need that.

Tod Larson · ‎11-01-2010

trace from the L2 switch on either end shows a first hop of the default gateway that is configured on the switch.

aqeel.karim · ‎11-01-2010

got'cha but the mac table should show the next hop address. I'm curious to know whether it is the routed or the switched interface. I'm checking some old sources, but I remember having my external interface with the with the psuedo wire and the inside connected to the L2.

Tod Larson · ‎11-01-2010

sh mac address-table has the desination port as the switch port connected to the router's xconnect interface.

aqeel.karim · ‎11-01-2010

Ok, so at least it is not going across the routed interface first. Brain storming... I will try and lab this up with GNS3 tonight and see what I can get.

aqeel.karim · ‎11-02-2010

Tod,

This is what I got from a co-worker who has extended what I did with L2TPv3, and made the single tun into a multi-point to pass multiple Vlans.

The Hub side is a 6509 w/ a 8-Port Gig Module

l2tp-class ESS

hello 10

password 7 111A180C1443595F

cookie size 8

pseudowire-class ETN_Support_Services

encapsulation l2tpv3

protocol l2tpv3 ESS

ip local interface Loopback0

ip dfbit set

interface GigabitEthernet0/1.30

description *** L2TP Termination for VLAN 30 ***

encapsulation dot1Q 30

no ip redirects

no ip proxy-arp

no cdp enable

xconnect X.X.47.42 1 encapsulation l2tpv3 pw-class ETN_Support_Services

Remote side is a C3845 w/ the std G0/0 and G0/1 int's.

l2tp-class ESS

hello 10

password 7 0017120F070A5955

cookie size 8

pseudowire-class ETN_Support_Services

encapsulation l2tpv3

protocol l2tpv3 ESS

ip local interface Loopback0

ip dfbit set

interface GigabitEthernet0/0.30

description *** Sub-Interface for VTC Network ***

encapsulation dot1Q 30

no ip redirects

no ip proxy-arp

no cdp enable

xconnect X.X.47.24 1 encapsulation l2tpv3 pw-class ETN_Support_Services

So, in comparison, the only diff I can see is that on your 7204 has a pure L3 interface. So, how did you get your G0/3 interface up without making sub-interfaces to pass L2 traffic?

Tod Larson · ‎12-30-2010

Turns out I was affected by this bug. An IOS update on my 7204 to 12.4.15T14 cleared it up.

http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCta91556