1. Packet Forwarding Flashcards
What is is the standard for VLAN?
802.1Q
What fields does VLAN packet contain?
- TPID
- PCP
- DEI
- VLAN ID
Where is VLAN 0 used for?
802.1P
Where is VLAN 1 used for?
Default VLAN
Where is VLAN 2 - 1001 used for?
Normal VLAN range
Where is VLAN 1002 - 1005 used for?
Reserved
Where is VLAN 1006 - 4096 used for?
Extended VLAN range
How is a VLAN created?
The command vlan id or name name
What must be done in order to process a VLAN change?
CLI must be placed back to global config mode
With what command can you change a port mode?
switchport mode …..
How many VLANs can be carried on a trunk port?
Multiple
How many VLANs can be carried on an access port?
1
How does a trunk port work?
Upon receipt:
- Examines headers
- Removes 802.1Q headers
- Forwarded out to the next port based on MAC
What is the native VLAN?
VLAN 1
When is traffic advertised/received on the native VLAN?
When there is no 802.1Q tag at the trunk port
What is the command to allow certain VLANs to travel accross the trunk port?
switchport trunk allowed vlan ….
What is the disadvantage of using the command switchport trunk allowed vlan ….?
It overwrites the list every time u use it
What is the MAC address table?
Responsible for identifying the switch ports and VLANs with which a device is associated. Resides in the CAM.
What is the CAM table?
Content Addressable Memory. It uses high-speed memory that is faster than typical computer RAM.
What is the ARP table?
Address Resolution Protocol. Provides a method of mapping L3 IP to L2 MAC.
Adds the L2 header and sends down to L2 for further processing
What is process switching?
When the general-purpose CPU on the router is in charge of packet switching
When is process switching preferred over CEF?
- When packets are to complex
- When packets require extra information (ARP)
What is Centralized Forwarding?
When a route processer is equipped with a forwarding engine
What is Distributed Forwarding?
When the line card is equipped with a forwarding engine
How does Centralized Forwarding work?
- Ingress
- Forwarding engine examens header
- Egress
How does Distributed Forwarding work?
- Ingress
- Forwarding engine does a lookup
- Local? –> local interface
- Outbound? –> backplane –> Egress
What does the software CEF consist of?
- Forwarding Information Base
- Adjacency table
What is SSO?
Statefull Switchover, a redundancy feature for routers with 2 routing processors
What is SDM template?
Switching Database manager, displayes ratios between CAM tables
