Catalyst Link-State Tracking

nospam@example.com (Zakir A. Khan, CCIE# 25121) — Sat, 13 Jun 2009 11:28:20 -0400

Catalyst 3750/3560 supports "Link-State Tracking". It is a simple and straightforward feature. First, some ports are defined upstream ports and some as downstream ports. Then, if all of the upstream ports go down, all the associated downstream ports are forced into the error-disabled (down) state automatically.

In the following example, if the upstream FastEthernet0/1 interface goes down, the downstream interface FastEthernet0/2 will go into a link down state.

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Stacked VLAN (Q-in-Q on a router)

nospam@example.com (Zakir A. Khan, CCIE# 25121) — Fri, 22 May 2009 20:11:32 -0400

A cisco router can be configured to do double tagging (Q-in-Q) on VLANs. Cisco calls it "Stacked VLAN Processing". Per cisco website, "A double-tagged, stacked VLAN frame is terminated or tunneled on an Ethernet subinterface by using the encapsulation dot1q second-dot1q command that specifies the two VLAN ID tags: an outer SP-VLAN ID and an inner CE-VLAN ID". So the command syntax for stacked VLAN is "encapsulation dot1q <outer-vlan-id> second-dot1q <inner-vlan-id>" or "encapsulation dot1q <sp-vlan-id> second-dot1q <ce-vlan-id>".

Ethernet subinterfaces on R1 are configured for the stacked VLAN processing. Here R1 is tagging inner VLANs 10 and 20 with outer VLAN 100 which is preserved all the way upto SW2's dot1q tunnel port (fa0/2). On fa0/2 port SW2 strips the outer VLAN 100 and sends the inner VLANs 10 and 20 to R2. The routers and switches are configured as following:

Continue reading "Stacked VLAN (Q-in-Q on a router)"

Zakir A. Khan - Bridging & Switching

Catalyst Link-State Tracking

Stacked VLAN (Q-in-Q on a router)