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So basically I'm having this issue while trying to configure the serial of 3 routers (router0, router1, router2) on Cisco Packet Tracer

I was able to configure both serials for router0 following this configuration:

Router(config)#interface serial 0/1/1 Router(config-if)#ip address 10.1.1.2 255.255.255.252

I have to clarify that router0 connects its serial 0/1/1 with serial 0/1/1 of router1

When I try to configure router1, I use this configuration:

Router(config)#interface serial 0/1/1 Router(config-if)#ip address 10.1.1.3 255.255.255.252

... but as soon as I hit enter it says "Bad mask /30 for address 10.1.1.3".

And yeah, that's my problem, the same issue happens if I try to configure router2.

This is the issue: This is the issue

This is the supposed configuration I have to follow This is the supposed configuration I have to follow

Paul
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Roy Najar
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1 Answers1

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10.1.1.3/30 is the directed broadcast address for that subnet and as such, it isn't usable as host address. You can use 10.1.1.1 and 10.1.1.2 from that subnet. If you do need to use 10.1.1.3 you need a shorter mask.

If your devices allow, you should consider using /31 subnets for point-to-point links. Both addresses in /31 are usable for host addressing, wasting none. /30 makes only 50% of the address range usable and is very wasteful.

Also, you don't need to use any addressing with physical point-to-point interfaces like serial since you can just route out of the port to reach the far side.

Zac67
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