On 06/20/2016 07:52 PM, Satish Patel wrote:
This is weird question but i thought let me get opinion from you guys.
We have following scenario
[ISP]------<Public-IP>-----[Router]-------<Private-IP>-------[L3
Switch]------------[Hosts]
In above diagram we get /24 subnet from ISP for hosts, Now i want to
configure routed network between [Router] and [L3 switch] so can i use
Private IP address (rfc1981) like 192.168.100.1/30 instead of Public
IP address, to save public IP address in point to point link. what
would be the disadvantage i will get doing that?
Well, if I understand your question, you want to put private IP's on the
point-to-points to save ip addresses. The only primary side-effect you
will have is for path mtu discovery - if the router or l3 switch needs
to fragment a packet for example (or send back any other icmp messages
like host unreachable or the like), it's likely to use the interface
address 'facing' the destination which would be your private IP's. These
are dropped by many firewalls and such, which effectively breaks path
mtu discovery and such. Depending on your equipment, you could assign 1
public IP to a loopback interface on the router and to the l3 switch,
which usually will cause that device to use that address as the source
for any icmp messages it generates.I am not %100 certain of the fine
details (would love someone to point out an authoratitive doc that
explains this for cisco), but I have used this method for exactly this
reason and it does seem to work.
Mike-
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