topic Re: Static route in Routing and SD-WAN

Static route

hussainabbas1442 — Tue, 01 Sep 2020 09:26:25 GMT

I have two routers in packet tracer

R1 and R2 having g0/1 ip address of 18.200.250.1 and 18.201.250.1 with both subnet mask of 255.255.255.0

Both routers have serial DCE cable connected

R1 with s0/0/1 with ip address of 192.168.2.1 255.255.255.252 and R2 with s0/0/0 with ip address 192.168.2.2 255.255.255.252

R2 has 2 loop addresses loop address 0, lo0 with ip address of 168.17.101.33 255.255.255.224 and loop address 1,lo1 with 168.17.101.65 255.255.255.224

Now i am trying to do static route on R1 for lo0 with next hop static route(recursive static route)

and directly connected static route on lo1 but not sure what command do i use for them both

I am confused and need help Thanks in advance 🙂

Re: Static route

Georg Pauwen — Tue, 01 Sep 2020 09:39:42 GMT

Hello,

what are you trying to configure ? What do you mean by 'directly connecte static route' ? Basically, whatever static route you configure, if you specify the other side of the serial link as next hop, that should be sufficient.

ip route 168.17.101.22 255.255.255.255 192.168.2.2

ip route 168.17.101.65 255.255.255.255 192.168.2.1

Re: Static route

hussainabbas1442 — Tue, 01 Sep 2020 10:19:18 GMT

Hi George,

I am trying to configure only on one router(R1)

When i wrote directly connected static route i meant command such as ip route 168.17.101.33 255.255.255.224 s0/0/1 (interface as an exit instead of ip address you might know this by other term) and when i write ip route 168.17.101.33 255.255.255.224 192.168.2.2 it gives me error Inconsistent address and mask and if the command is

ip route 168.17.101.65 255.255.255.224 s0/0/1 it gives me error Default route without gateway, if not a point-to-point interface, may impact performance so i felt my command is wrong

Re: Static route

hussainabbas1442 — Tue, 01 Sep 2020 10:26:05 GMT

Hi George, I have replied to your message in the post above

Re: Static route

Giuseppe Larosa — Tue, 01 Sep 2020 10:27:16 GMT

Hello @hussainabbas1442 ,

when you configure static routes you need to refer to the subnet address and not the address on the loop0/loop1 of the other router.

so you should use

ip route 168.17.101.32 255.255.255.224 192.168.2.2

this should be accepted

the second static route should be:

ip route 168.17.101.64 255.255.255.224 s0/0/1

it will give you the same warning but a serial interface is a p2p link. ! The warning applies to LAN interface where proxy ARP would be involved causing excessive ARP activity when compared to the use of an IP next-hop.

Hope to help

Giuseppe

Re: Static route

Georg Pauwen — Tue, 01 Sep 2020 10:30:42 GMT

Hello,

--> ip route 168.17.101.33 255.255.255.224 192.168.2.2 it gives me error Inconsistent address and mask

You need either one of the below:

ip route 168.17.101.32 255.255.255.224 192.168.2.2

ip route 168.17.101.33 255.255.255.255 192.168.2.2

--> ip route 168.17.101.65 255.255.255.224 s0/0/1 it gives me error Default route without gateway, if not a point-to-point interface, may impact performance so i felt my command is wrong

This is not an error, just a warning. On point to point links, it is recommended to use the next hop IP address rather than the outgoing interface. This is because when you use the outgoing interface, the router has to ARP for the other side.

Re: Static route

hussainabbas1442 — Tue, 01 Sep 2020 11:00:25 GMT

Hi @Giuseppe Larosa

It does work thanks but why .32 and .64

Re: Static route

hussainabbas1442 — Tue, 01 Sep 2020 11:01:26 GMT

Hi @Georg Pauwen

Thank you.

Re: Static route

Giuseppe Larosa — Tue, 01 Sep 2020 12:13:50 GMT

Hello @hussainabbas1442 ,

the .32 and .64 are the subnet addresses that is given a subnet mask of 255.255.255.224 it identifies an host portion made of the last 5 bits.

In the subnet address all the host bits are 0

so you get

168.17.103.32/27 subnet mask 255.255.255.224

168.17.103.64/27 subnet mask 255.255.255.224

to be noted both the subnet adddress ( all zero in host portion) and the subnet broadcast address ( all ones in the host portion) are reserved and cannot be assigned to an host including a loopback interface.

So for subnet 168.17.103.32/27 subnet mask 255.255.255.224

the first usable address is 168.17.103.33 and the last usable address is 168.17.103.62

with 168.17.103.63 being the subnet directed broadcast address.

Static routes refer to subnets or prefixes so for non host routes ( subnet mask different from 255.255.255.255) you need to refer to the correct subnet address when configurig the static routes. The router CLI parser checks that the specified address and subnet mask are compatible.

Hope to help

Giuseppe