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Router on Stick, L3 Switches

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beef410's version from 2018-04-05 13:30

Router setup

Question Answer
Router SubIntsLogical interfaces splitting physical interface up so vlans can use their vlan network IP. Good practice is for subint number to match the vlan number
HostsMust use their vlans network IP as default gateway to reach correct subint
Order of commandsMust configure subint with 802.1q/ISL before adding IP
(config-subif)#encap <dot1q/isl> <vlanID>Pick a vlan protocol encap type and its vlan ID
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L3 Switch SVI

Question Answer
SVISwitch Virtual Interfaces, L3 switch version of a subint.
(config)# int vlan #creates SVI, give it the relevant network ip addr
HostsSet default gateway to be relevant vlan ip.
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L3 Switch Routed Port

Question Answer
FeaturesSVI's and routed ports are not mutually exclusive. Turns switchport into a router port IE default gateway port which the switch will see the port as a connected route. Need to enable routing protos
(config)#ip routingenable routing on the switch
Order mattersEnable routing, turn switchport into a routed port, give it an ip
(config-if)# no switchportLine protocol will cycle and the port will become routed
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L3 Switch Etherchannels

Question Answer
Step 0Enable IP routing on the switch
Step 1Enable routing on the ports, turn on routed port. no switchport. Cycles the ports
Step 2Add channel-group # mode <> to ports, no switchport after this will remove channel-group command
Step 3Create port-channel as routed port/noswitchport and give it an IP
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Troubleshoot

Question Answer
Subint is downProbably missing encapsulation command or physical interface is shut
Ping verificationStart from spoke host and if failure continue pulling back one hop at a time until you're back to ping your default gateway
Config verificationencap command must match intended vlan and thus match the ip addr assigned to said vlan. Check IP's first
Can't pingEnsure L3 switch has a routing protocol enabled
sh port-channel, not-connectno switchport command will remove the L2 channel-group command. Issue with converting L2 to L3 etherchannel
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