Configuring ISL Trunking Cisco Catalyst Switch

Configuring ISL Trunking Cisco Catalyst Switch networkingguruji1.com/2019/12/configuring-isl-trunking-cisco-catalyst-switch.html

My Dear Friend in today’s article, I will tell you “Configuring ISL Trunking cisco catalyst switch” If you any problem after reading this article, you can see the video below. Please don't forget to Like, Share, Comment & Subscribe to our Networking Guruji Channel for more video.

Cisco switch uses two encapsulations on the trunk port.

---- ISL (Inter-Switch Link) ---- Dot1q/802.1q -- 802.1q Open Standard -- ISL Cisco Proprietary

Today discussion only ISL Trunking.

ISL -ISL is a Cisco proprietary protocol.

- Supports up to 1000 VLANs - The original frame is encapsulated and a new header is inserte encapsulation process.

- A 26-byte header and a 4 byte FCS (frame check sequence) are inserted. Hence a total of 30 bytes of overhead.

- ISL tags native VLANs. v Statically set the trunking encapsulation on SW-1 inter-switch to ISL. v Verify that SW-2 and SW-3 are negotiated as trunking encapsulation to SW-1 and that SW1 is negotiating ISL to SW-2 and SW-3.

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ISL Trunk Configuration SW-1 SW-1(config)#interface fastethernet 0/1 SW-1(config-if)#switchport trunk encapsulation isl SW-1(config)#interface fastethernet 0/2 SW-1(config-if)#switchport trunk encapsulation isl Verification & Expiation: Sw-1 inter-switch links are running DTP Desirable mode (initiating trunking) with ISL encapsulation statically set. “Inter-Switch Link (ISL)� This can be seen under the mode and encapsulation column from show interface trunk output.

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SW-1#Show interface trunk Port Mode Fa0/1 desirable Fa0/2 desirable Port Fa0/1 Fa0/2 Port Fa0/1 Fa0/2 Port Fa0/1 Fa0/2

Encapsulation isl isl

Status trunking trunking

Native vlan 1 1

Vlans allowed on trunk 1-1005 1-1005 VLANs allowed and active in management domain 1 1 VLAN in spanning tree forwarding state and not pruned none none

“Cisco CCNA ISL Configuration� SW-2 and SW-3 inter-switch are in DTP auto mode which means they will accept negotiation to from the trunk but will not initiate negotiation. Since SW-1 is statically set to ISl encapsulation SW-2 and SW-3 must agree to this or DTP negotiation will fail. A successful negotiation will be seen in this output since the 3/4

encapsulation is n-isl, for negotiated ISL. SW-1#Show interface trunk Port Mode Encapsulation Status Native VLAN Fa0/2 auto n-isl trunking 1 Port VLANs allowed on trunk Fa0/2 1-1005 Port VLANs allowed and active in management domain Fa0/2 1 Port VLAN in spanning-tree forwarding state and not pruned Fa0/2 1

SW-1#Show interface trunk Port Fa0/1 Port Fa0/1 Port Fa0/1 Port Fa0/1

Mode Encapsulation Status Native VLAN auto n-isl trunking 1 Vlans allowed on trunk 1-1005 VLANs allowed and active in management domain 1 VLAN in spanning-tree forwarding state and not pruned 1

This is the full article “Configuring ISL Trunking cisco catalyst switch� Thank you so much.

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