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Use of /31 subnetmask on Point to point link-Part2

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					Use of ‘/31 IP subnet’ on point to point links; and their effect on routing
protocols –Part2

I got a query whether /31 subnet would affect routing protocols on other devices, not just the
Cisco I tested previously. You can refer same at
(http://www.docstoc.com/docs/130412142/Use-of-‘31-IP-subnet’-on-point-to-point-links-and-
their-effect-on-routing-protocols).

Let’s review the topology I used before for test.




R2 is going to be a Cisco 3560 and R1 for now is a Juniper SSG5.

Quick configs.

JUNIPER SSG:                                           CISCO :
set interface ethernet0/0 ip 10.1.1.2/31               interface Loopback0
set interface ethernet0/0 route                        ip address 192.168.1.1 255.255.255.0
set interface loopback.1 ip 172.16.1.1/24              !
set interface loopback.1 route                         interface FastEthernet0/1
!                                                      no switchport
set access-list 10                                     ip address 10.1.1.3 255.255.255.254
set access-list 10 permit ip 172.16.1.0/24 10          !
set route-map name "p" permit 10                       router ospf 1
set match interface ethernet0/0 loopback.1             redistribute connected subnets
set match ip 10                                        network 10.1.1.3 0.0.0.0 area 0
!
set interface ethernet0/0 protocol ospf area 0.0.0.0
set interface ethernet0/0 protocol ospf enable
set interface loopback.1 protocol ospf area 0.0.0.0
set interface loopback.1 protocol ospf enable
Are they neighbours?

JUNIPER SSG:

ssg5-serial-> get interface eth0/0 protocol ospf
VR: trust-vr RouterId: 192.168.2.1
----------------------------------
Interface: ethernet0/0
IpAddr: 10.1.1.2/31, OSPF: enabled, Router: enabled
Type: Broadcast Area: 0.0.0.0 Priority: 1 Cost: 1 Passive: No
Transit delay: 1s Retransmit interval: 5s Hello interval: 10s
Router Dead interval: 40s Authentication-Type: None
Ignore-MTU: no Reduce-flooding: no
State: Backup Designated Router DR: 10.1.1.3 BDR: 10.1.1.2(self)
Neighbors:
RtrId: 10.1.1.3 IpAddr: 10.1.1.3 Pri: 1 State: Full

CISCO :
Switch#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
192.168.2.1 1 FULL/BDR 00:00:34 10.1.1.2 FastEthernet0/1
Finally, can they see the routes and ping the loopbacks?

JUNIPER:
ssg5-serial-> get route
IPv4 Dest-Routes for (0 entries)
--------------------------------------------------------------------------------------
H: Host C: Connected S: Static A: Auto-Exported
I: Imported R: RIP P: Permanent D: Auto-Discovered
N: NHRP
iB: IBGP eB: EBGP O: OSPF E1: OSPF external type 1
E2: OSPF external type 2 trailing B: backup route
IPv4 Dest-Routes for
(6 entries)
--------------------------------------------------------------------------------------
ID IP-Prefix Interface Gateway P Pref Mtr Vsys
--------------------------------------------------------------------------------------
* 9 10.1.1.2/32 eth0/0 0.0.0.0 H 0 0 Root
* 8 10.1.1.2/31 eth0/0 0.0.0.0 C 0 0 Root
* 3 172.16.1.0/24 loopback.1 0.0.0.0 C 0 0 Root
* 5 192.168.2.1/32 eth0/5 0.0.0.0 H 0 0 Root
* 4 192.168.2.0/24 eth0/5 0.0.0.0 C 0 0 Root
* 11 192.168.1.0/24 eth0/0 10.1.1.3 E2 200 20 Root
ssg5-serial-> ping 192.168.1.1
Type escape sequence to abort
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 1 seconds
!!!!!
Success Rate is 100 percent (5/5), round-trip time min/avg/max=2/3/4 ms
CISCO :
Switch#sh ip route
172.16.0.0/24 is subnetted, 1 subnets
O 172.16.1.0 [110/2] via 10.1.1.2, 00:12:37, FastEthernet0/1
10.0.0.0/31 is subnetted, 1 subnets
C 10.1.1.2 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, Loopback0
Switch#ping 172.16.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/9 ms
To be honest, I’m not even going to bother with RIP. I never use it, so what for?
We use Foundry/Brocade routers as well, so how do they hold up?

FOUNDRY CONFIG:
SSH@foundry(config-if-e1000-1/6)#ip address 10.1.1.2/31
IP/Port: Errno(9) Cannot assign broadcast address
SSH@foundry(config-if-e1000-1/6)#ip address 10.1.1.3/31
IP/Port: Errno(9) Cannot assign broadcast address
SSH@foundry(config-if-e1000-1/6)#ip address 10.1.1.4/31
IP/Port: Errno(9) Cannot assign broadcast address

The Foundry won’t even allow me to assign the IP address. As a note I’m using fairly recent
code:

SL M1: NI-XMR-MR Management Module Active (Serial #: XXXXXXXXX, Part #: XXXXX-XXXX):
Boot : Version 5.0.0T165 Copyright (c) 1996-2009 Brocade Communications Systems,
Inc.
Compiled on Apr 19 2010 at 17:27:10 labeled as xmprm05000
What about JUNOS itself?
Juniper config:
root> show configuration
version 7.1R2.2;
interfaces {
fxp0 {
unit 0 {
family inet {
address 10.1.1.2/31;
}
}
}
lo0 {
unit 0 {
family inet {
address 172.16.1.1/32;
}
}
}
}
protocols {
ospf {
area 0.0.0.0 {
interface 10.1.1.2;
interface 172.16.1.1;
}
}
}
Cisco same as the previous examples.

Neighbours?
JUNOS:
root> show ospf neighbor
Address Interface State ID Pri Dead
10.1.1.3 fxp0.0 Full 192.168.1.1 1 39

CISCO :
Router#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
172.16.1.1 128 FULL/DR 00:00:38 10.1.1.2 FastEthernet0/1

Routes?
JUNOS:
root> show route
inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.1.1.2/31 *[Direct/0] 00:08:12
> via fxp0.0
10.1.1.2/32 *[Local/0] 00:08:12
Local via fxp0.0
172.16.1.1/32 *[Direct/0] 00:06:03
> via lo0.0
192.168.1.1/32 *[OSPF/10] 00:03:26, metric 2
> to 10.1.1.3 via fxp0.0
root> ping 192.168.1.1 count 5
PING 192.168.1.1 (192.168.1.1): 56 data bytes
64 bytes from 192.168.1.1: icmp_seq=0 ttl=255 time=1.250 ms
64 bytes from 192.168.1.1: icmp_seq=1 ttl=255 time=1.273 ms
64 bytes from 192.168.1.1: icmp_seq=2 ttl=255 time=1.222 ms
64 bytes from 192.168.1.1: icmp_seq=3 ttl=255 time=1.267 ms
64 bytes from 192.168.1.1: icmp_seq=4 ttl=255 time=1.215 ms
--- 192.168.1.1 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max/stddev = 1.215/1.245/1.273/0.023 ms

CISCO :
Router#sh ip route
Gateway of last resort is not set
172.16.0.0/32 is subnetted, 1 subnets
O 172.16.1.1 [110/1] via 10.1.1.2, 00:04:18, FastEthernet0/1
10.0.0.0/31 is subnetted, 1 subnets
C 10.1.1.2 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, Loopback0
Router#ping 172.16.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
Most seem to work. I’m a bit upset about the Brocade/Foundry result though!

				
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