What is the IP of the router that connects to this router?
It must be an IP address in the same subnet. Other than that, the network designer has the flexibility to assign any IP address in the same subnet. Quite often, the first or last IP addresses in a subnet are used, so if a certain interface on this router has IP address 10.0.5.1, and the network mask is 255.255.255.0, I would strongly suspect that the other router has IP address 10.0.5.2 (10.0.5.0 can't be used for this subnet).For serial (point-to-point) connections, to save address space, quite often a subnet /30 is used (that is, a subnet mask of 255.255.255.252), in which case the other router has the only other usable IP address in the subnet. For example, if this router has IP address 10.0.8.26 and a subnet mask 255.255.255.252, the subnet has addresses in the range 10.0.8.24 - 10.0.8.27, but since the first and last addresses can't be used, the only option for a router or other machine on the other end is 10.0.8.25.It must be an IP address in the same subnet. Other than that, the network designer has the flexibility to assign any IP address in the same subnet. Quite often, the first or last IP addresses in a subnet are used, so if a certain interface on this router has IP address 10.0.5.1, and the network mask is 255.255.255.0, I would strongly suspect that the other router has IP address 10.0.5.2 (10.0.5.0 can't be used for this subnet).For serial (point-to-point) connections, to save address space, quite often a subnet /30 is used (that is, a subnet mask of 255.255.255.252), in which case the other router has the only other usable IP address in the subnet. For example, if this router has IP address 10.0.8.26 and a subnet mask 255.255.255.252, the subnet has addresses in the range 10.0.8.24 - 10.0.8.27, but since the first and last addresses can't be used, the only option for a router or other machine on the other end is 10.0.8.25.It must be an IP address in the same subnet. Other than that, the network designer has the flexibility to assign any IP address in the same subnet. Quite often, the first or last IP addresses in a subnet are used, so if a certain interface on this router has IP address 10.0.5.1, and the network mask is 255.255.255.0, I would strongly suspect that the other router has IP address 10.0.5.2 (10.0.5.0 can't be used for this subnet).For serial (point-to-point) connections, to save address space, quite often a subnet /30 is used (that is, a subnet mask of 255.255.255.252), in which case the other router has the only other usable IP address in the subnet. For example, if this router has IP address 10.0.8.26 and a subnet mask 255.255.255.252, the subnet has addresses in the range 10.0.8.24 - 10.0.8.27, but since the first and last addresses can't be used, the only option for a router or other machine on the other end is 10.0.8.25.It must be an IP address in the same subnet. Other than that, the network designer has the flexibility to assign any IP address in the same subnet. Quite often, the first or last IP addresses in a subnet are used, so if a certain interface on this router has IP address 10.0.5.1, and the network mask is 255.255.255.0, I would strongly suspect that the other router has IP address 10.0.5.2 (10.0.5.0 can't be used for this subnet).For serial (point-to-point) connections, to save address space, quite often a subnet /30 is used (that is, a subnet mask of 255.255.255.252), in which case the other router has the only other usable IP address in the subnet. For example, if this router has IP address 10.0.8.26 and a subnet mask 255.255.255.252, the subnet has addresses in the range 10.0.8.24 - 10.0.8.27, but since the first and last addresses can't be used, the only option for a router or other machine on the other end is 10.0.8.25.
Rene
Ezra
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