Term
| command to add a static arp entry |
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Definition
| arp 150.1.6.6 0011.93da.bf40 arpa |
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Term
| command to restore default proxy arp settings on an interface |
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Definition
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Term
| why is it a bad idea to point a default route at an interface only? |
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Definition
| because a separate arp request will be required for every final destination IP that matches the default route. |
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Term
| commands to view arp table and see if an arp request is failing in real time |
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Definition
sh arp
debug arp
debug ip packet |
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Term
| what are the only interface types that you should point a static route to i.e. no next-hop IP? |
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Definition
| any point-to-point e.g. GRE, PPP or HDLC. |
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Term
| what is the behaviour of a static route that is configured with only a next-hop value? |
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Definition
| the route is valid as long as a route exists for the next-hop. |
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Term
| what is the behaviour of a static route that is configured with only an outgoing interface? |
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Definition
| the route is valid as long as the interface is UP/UP. |
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Term
| what is the behaviour of a static route that is configured with both a next-hop and an outgoing interface? |
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Definition
| the route is valid as long as the next-hop is available via the stated interface. |
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Term
| what is required for static routes over an MGRE interface on a DMVPN spoke? |
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Definition
| a next-hop, interface or both can be used. |
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Term
| what is required for static routes over an MGRE interface on a DMVPN hub? |
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Definition
| a next-hop must be specified. |
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Term
| when a static route only points to an MGRE interface on a DMVPN hub, what 2 methods can be used to forward traffic to a spoke. |
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Definition
1. specify the next-hop on the routes.
2. add static NHRP mappings for the final destination IPs. |
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Term
| command to confirm what interface a packet will be forwarded to. |
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Definition
| sh ip cef x.x.x.x internal |
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Term
| what will happen to a static route that recurses to an interface in the UP/DOWN state? |
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Definition
| it will not be placed in the routing table. |
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Term
| command to view active and non-active static routes |
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Definition
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Term
| why is it a bad idea to rely on interface status to determine if a route is valid? |
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Definition
| it only confirms L2 status, not L2 connectivity. If a switch separates 2 routers, one will not detect the others' link failure, which could lead to blackholed traffic. |
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Term
| 2 methods to overcome the limitations of relying on interface status to validate static routes. |
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Definition
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Term
| how can you configure a router to forward traffic without even consulting the routing table? |
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Definition
| using policy-based routing. |
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Term
| 2 commands to confirm that policy routing is configured on an interface. |
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Definition
sh ip policy
sh ip inter | i Policy |
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Term
| command to confirm that packets are being policy routed |
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Definition
sh route-map
look for packet matches. |
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Term
| commands to make PBR reliable, using enhanced object tracking. |
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Definition
set ip next-hop verify-availability x.x.x.x 1 track 1
set ip default next-hop y.y.y.y |
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Term
| commands to make PBR reliable, using CDP |
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Definition
set ip next-hop x.x.x.x
set ip next-hop verify-availability
set ip default next-hop y.y.y.y |
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Term
| commands to verify ip sla config and its state |
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Definition
sh ip sla config
sh ip sla statist |
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Term
| command to verify the state of an enhanced object |
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Definition
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Term
| command to apply a policy routing to traffic generated by the router. |
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Definition
| ip local policy route-map POL_RM |
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Term
| why might traffic forwarded based on a local policy have source IP inconsistencies? |
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Definition
| because the routing table is not consulted, therefore the router might not source the packet from the outgoing interface. |
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Term
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Definition
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Term
| when configuring a GRE interface, by how much is the MTU of the tunnel interface automatically lowered? |
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Definition
24 bytes total.
New IP header 20 bytes.
GRE header 4 bytes. |
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Term
| 2 symptoms of a tunnel recursive routing issue. |
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Definition
1. flapping tunnel interface.
2. an obvious error message. |
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Term
| 4 methods to avoid tunnel recursive routing issues. |
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Definition
1. don't advertise underlay & overlay in same routing protocol.
2. don't advertise tunnel endpoints in the overlay.
3. filter tunnel endpoints from overlay if necessary.
4. don't use same routing protocol in underlay/overlay |
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Term
| interface commands to configure a backup tunnel interface that will be enabled 5 secs after primary failure. Backup should be deactivated 60 secs after primary is restored. |
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Definition
backup interface Tunnel2
backup delay 5 60 |
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Term
| command to verify backup config. |
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Definition
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Term
| 2 rules when configuring backup interfaces. |
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Definition
1. primary must be P2P interface type.
2. backup can't be a subinterface, but it can be a tunnel assigned to a subinterface. |
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Term
| why might backup interfaces for a tunnel be reliable and how can you overcome this? |
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Definition
| tunnels will be always up if a route exists to the destination IP, there is a danger of blackholes. Configure tunnel keepalives for reliability. |
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Term
| command to send 1 tunnel keepalive every second and allow for 3 retries. |
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Definition
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Term
| why do tunnel keepalives not work with MGRE? |
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Definition
| because no tunnel destination is defined. |
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Term
| how can keeplives be used to help with MGRE reliability? |
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Definition
| a regular gre tunnel could be configured using the samed endpoints as the MGRE. This could use keepalives to to trigger a backup tunnel with a more preferable floating static route. |
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Term
| command to view backup operation in real-time. |
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Definition
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Term
| what does ODR use to disseminate routing info? |
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Definition
| CDP - make sure this is enabled. |
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Term
| when "router odr" is configured on a hub, what will the spokes (stub routers) advertise? |
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Definition
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Term
| what condition must be met on the stub routers for ODR to work? |
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Definition
| no routing protocols must be configured. |
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Term
| what is the admin distance of an ODR route? |
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Definition
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Term
| command to ensure odr is enabled on a router |
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Definition
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Term
| how to prevent traffic blackholing with ODR. |
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Definition
| ensure CDP is not advertising connected routes via interfaces other than what is intended. |
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