notes: PPP Peer neighbhor route

A /32 is automatically created for neighbor routes by default.

- It automatically sets up a route to the peer address on a point-to-point interface when the PPP IPCP negotiation is completed.

- It is useful to provide reachability when both ends of the PPP link are not on the same logical subnet. ie IP-unnumbered.

- Can be safely disabled when both ends of the link are in the same logical subnet.
- If using IP-unnumbered or dissimilar IP subnets on a data-link, leave it enabled.

- Most commonly used when different IP subnets on the same physical segment.
> R1 S1/0 is directly connected to R2 S2/0.
> R1 S1/0: IP address is 4.4.4.4/24.
> R2 S2/0: IP address is 5.5.5.5/24.
> R2 will have 4.4.4.4 in the routing table as 4.0.0.0/8 and 4.4.4.4 will be pingable.
> R1 will have 5.5.5.5 in the routing table as 5.0.0.0/8.
> Problems is that only the IP address is advertised to a PPP neighbor, and not the SUBNET MASK, it will assume classful boundary.

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COMMANDS
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interface E0
no peer neighbor-route

- Disables peer neighbor route, then connected IP address won’t be advertised
- Disables /32 host routes for the interface