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Helpful
9
Replies

Broad Ip route statemwnt with smaller detailed IP route under

sejamc71
Beginner
Beginner

Maybe dumb question, but at some point in time, a previous network engineer defined a machine network as 10.100.1.0 255.255.0.0 when it should have been 255.255.255.0. It was in place for several years and there are several hundred PLC devices now configured that way. My other remote sites have PLC subnets of 10.100.5.0 255.255.255.0, 10.100.6.0 255.255.255.0 and so on. In my core, can I do broad

IP route

statement with smaller

ip route

statement subnets under it or above it?

ip route 10.100.5.0 255.255.255.0 172.16.1.14

ip route 10.100.6.0 255.255.255.0 172.16.1.14

ip route 10.100.7.0 255.255.255.0 172.16.1.14

ip route 10.100.0.0 255.255.0.0 172.16.12.25

 

2 Accepted Solutions

Accepted Solutions

If it mater of static route'

Then config order not important to router 

The router will select longest path in rib'

So always .5/24 .6/24 .7/24 longest than .0/16

View solution in original post

I run lab test static router  there is no issue.

Screenshot (847).png

Screenshot (848).png

View solution in original post

9 Replies 9

If it mater of static route'

Then config order not important to router 

The router will select longest path in rib'

So always .5/24 .6/24 .7/24 longest than .0/16

I should also include that 10.100.0.0 255.255.0.0 is a subnet at a local plant and the others 10.100.5.0, 10.100.6. and etc are routed to the firewall and are remote.

So you think this should work?

For static route it work but 

You will face many issue with conflict IP in site and

HQ

For example pc in

 HQ 

have

ip 10.100.7.1

 

Which is same IP of host in other site .7/24 

So overlapping happened sure.

There some solution like use

 NAT

https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/13774-3.html

At the

HQ

plant site, they only use 10.100.1.0 - 10.100.4.254 so even though they technically could assign a

10.100.7.1 IP,

there is no DHCP, they wouldn't assign that IP statically at the

HQ.

I've wanted to change it, but there are literally 700 or so devices that they would need to manually change on the plant production side

That good if

HQ

use from .0 ip to .4

But pc in

HQ

get ip from DHCP with 

10.100.x.x/16

Now this pc need to connect to 10.100.5.100 

The pc not send this traffic to GW' the pc with subnet and subnet mask receive from dhcp assume that 10.100.5.100 in same subnet and send

arp ask IP-MAC'

here the connection is failed.

So using

NAT

or change site SuperNer (instead of 10.100 let be 10.101) is better.

there is no dhcp on the 10.100.xxx.xxx subnets. Anything on these subnets for the local and remote locations has to be manually assigned. These specific networks are also blocked from any internet access

 

I clear some points yoh will face' I will run also lab and update you other issue appear with this subnet overlapping.

In my lab I will use only static route.

MHM

I run lab test static router  there is no issue.

Screenshot (847).png

Screenshot (848).png

Hello
those static routes look okay - the longer static statements /24 point to a different next hop then the shorter /16 which is applicable meaning any packet not matching any of the /24 routes will be routed via the /16 route


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Kind Regards
Paul
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