L2 Trunking and Tunneling Notes

Ethernet:

802.1q tunneling  mainly used in  Core

Layer2 Security:

port security, PVLANS, VACLS, DHCP Snooping, etc.

Layer 2 QoS.

Classification, Marking, Policing, Queueing, etc

Ethernet Interface Types.

Layer 2 Switch ports

- Access  ie one vlan

interface f 0/1

switchport mode access

switchport access vlan 10

- Trunk == multiple VLANS

ISL is cisco propriety

All traffic encapsulated with ISL

802.1q

open standard

native vlan sent untagged.

DTP (dynamic trunking protocol)

Used to automatically negotiate what are trunk links supposed to be.

verified with ..

show interface trunk

show interface switchport

show spanning-tree [vlan | interface]

desirable mode == initiates trunking negotiation

auto mode = passively listen for trunking negotiation

Disabling DTP negotiation

Switch port non-negotiate

Switch port mode access

Switch port mode dot1q-tunnel

- Tunnel = transparent Layer 2 VPN

- Dynamic = DTP negotiation

Layer 3 Ports

- Switched Virtual Interface (SVI)

- Native Routed Interface

802.1q Tunneling

==================

1. Layer 2 VPN over switched ethernet network

Lightweight version of MPLS L2VPN

2. SP's PE adds additional 802.1q tag to all frames received from CE

called "metro tag" or "QinQ"

3. PE assigns all CE facing ports to the same VLAN

One vlan per customer in P network.

Configuration

-switchport mode dot1q-tunnel

tell switch to double tag frames

-switchport access vlan {vlan}

metro vlan assignment

Verification

-show dot1q-tunnel

Cannot be dynamically negotiated.

802.1q Tunneling Design Issues:

================================

Assumes L2 network end to end

- PE - P - PE links must all run layer 2 trunking

- Implies scalability issues.

Additional tags increase payload size

- 4 bytes per tag

- potential to exceed MTU of the transit path

- Ethernet doesn't support fragmentation

Loass of control plane signaling for CE devices

- CDP, VTP, STP etc dropped by PE.

Layer 2 Protocol tunneling

==========================

used to tunnel layer 2 control plane protocols between ports

-used with 802.1 q tunnel

Support for .. -cdp, vtp, stp, PAgP, LACP, and UDLD.

EtherChannel over 802.1q Tunnels

===================================

CE can suppport aggregation of CE-PE links

eg 2*GigE per customer site

EtherChannel must be point to point

- Implies one metro tag per PE-CE link

PE can tunnel negotiation as well

-l2protocol-tunnel point-to-point [lacp | pagp]