Network Theory - IP operations - ICMP unreachable, redirect

10 important questions on Network Theory - IP operations - ICMP unreachable, redirect

What does "icmp unreachable" mean and what is the default?


ICMP unreachable notifies the sender if the router receives a packet it cannot deliver to the destination as it does not have a route to it.

Default enabled on a switch/router

What does the command (config)# ip icmp rate-limit unreachable [df] milliseconds mean?


rate limit ICMP destination unreachable messages

What is the command to disable icmp redirect and what is the default?

Default enabled

(config-if)#no ip redirects
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What is not reachable with ICMP type 3 code 3?

TCP port unreachable (used with traceroute)

What is not reachable with ICMP type 3 code 4?

Fragment needed but DF was set

What is not reachable with ICMP type 3 code 5?

Source routing

Used when packets must take configured hops (loose,strict routing)

What is ICMP type 3 code 9,10,13 used for?

Used if something is prohibited with access-lists deny

What is ICMP type 3 code 11,12,14,15 used for?

Used for QOS with tos, ip-precedence

What command can be used to test UDP port on a host?

Use trace command

11. IP Oper. - ICMP Unreachables 8:22

What are the questions when a router sends a redirect?

Is route out the same interface?
Are IP redirects enabled?
Is source IP from same network as the better next hop?

14. ICMP Redirects 7:40

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