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Category: CCNA

Tclsh script examples: how to generate router loop interfaces with IPv4 addresses

This example shows how to generate 254 loop interfaces with assigned ipv4 addresses up to The code is:

for {set i 0} {$i < 256} {incr i} {
ios_config "int loop $i" "ip address 172.16.$i.1"
ios_config "end"

and you may just simply copy and paste it into a Cisco router CLI. Therefore first run tclsh within of privileged EXEC mode

Possible bugs/limitations encountered in Cisco’s RIP implementation

  1. Default route origination not working reliably.
  2. Automatic summarization turned on causes major networks to be propagated throughout the RIP domain with a metric of 1.
  3. Using RIPv2 on NBMA hub-and-spoke topology causes the hub router to rewrite the next hop field in the RIPv2 update to the IP address of the spoke router advertising the originalupdate, thereby creating reachability issues