Lessons Learned:
RIP Auto-summary
RIPV1 – is default
when configuring RIP
RIPv2 is classless but does automatic classful summarization
by default.
-Disabled with no auto-summary
VLSM is supported within
the same major network.
Advertisements between
major network boundaries are summarized to classful boundary
-Can result in traffic black holes.
Split Horizon –
If enabled will stop
routes from being sent back out the interfaces they we’re learned on.
RIP is a distance vector protocol.
Updates received in an interface will not be sent back out
the same interface.
Basically if you advertise a route to me, I don’t want to
send the same route back to you. This could result in a loop in the data-plane.
-Undesirable on partial mesh NBMA networks.
Enabled by default on all interfaces except main interface
in Frame Relay. It will be enables on all other interfaces.
Ex: in multipoint it would be enabled
on the sub interfaces.
-no ip split-horizon to disable,
Verifcation
#sh ip interface
This is show if Split horizon is enabled on the interface.
Note: remember once a RIP route has been down for over 240
seconds they will be removed from the routing table.
We can also use the debug IP RIP to see what routes are being
advertised. And what is being received.
R1#sh ip interface
fa0/0
FastEthernet0/0 is up, line protocol is up
Internet address is
192.168.12.1/24
Broadcast address is
255.255.255.255
Address determined
by non-volatile memory
MTU is 1500 bytes
Helper address is
not set
Directed broadcast forwarding is disabled
Multicast reserved
groups joined: 224.0.0.9
Outgoing access list
is not set
Inbound access list is not set
Proxy ARP is enabled
Local Proxy ARP is
disabled
Security level is
default
Split horizon is enabled –
Split Horizon is enabled.
ICMP redirects are
always sent
ICMP unreachables
are always sent
ICMP mask replies
are never sent
IP fast switching is
enabled
IP fast switching on
the same interface is disabled
IP Flow switching is
disabled
IP CEF switching is
enabled
IP CEF Fast
switching turbo vector
IP multicast fast
switching is enabled
Debug IP RIP :
*Mar 1 00:04:42.303:
RIP: sending v2 update to 224.0.0.9 via FastEthernet0/0 (192.168.12.1)
*Mar 1 00:04:42.307:
RIP: build update entries
*Mar 1 00:04:42.307: 10.1.1.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 1 00:04:43.075:
RIP: sending v2 update to 224.0.0.9 via Loopback1 (10.1.1.1)
*Mar 1 00:04:43.079:
RIP: build update entries
*Mar 1
00:04:43.079: 192.168.12.0/24 via
0.0.0.0, metric 1, tag 0
*Mar 1 00:04:43.091: RIP: ignored v2 packet from
10.1.1.1 (sourced from one of our addresses) – shows split horizon at work – the
update is not process and the route is ignored
Debug IP routing – will show any and all maintenance on the
routing itself.
RIP Convergence Timers:
Global – will affect all interfaces
-Timers basic (update) (invalid) (Holddown) (flush)
Interface level – will affect just the interface.
-#ip rip advertisement (interval)
Note: All the timers start
counting at the same time index. The default is 30 seconds.
Once a router receives an update in
, the rest of it’s timers which are the invalid, hold down, and flush timers. These
all start counting up.
Basically from the last time the
router received an update, if the time gets to 180 seconds, the route becomes “invalid”
and it goes into “hold down”. Most of
the time the invalid and hold down have the same value. Technically they have two different purposes.
The hold down says – when I receive
a new update in regarding a prefix, only accept it if it has the same or better
metric. To verify the routing information is not looping around the network
while its aging out.
The Invalid says – the route is
possibly down in the routing table.
Flush timer is 240 sec by default,
if it does past that time –remove the route.
Verify the timers:
# sh ip protocols
R3#sh ip protocols
Routing Protocol is
"rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 30 seconds,
next due in 16 seconds – send updates
Invalid after 180 seconds, hold
down 180, flushed after 240 – invalid, hold, and flush
Redistributing: rip
Default version control: send version 2, receive version 2
Interface Send Recv
Triggered RIP Key-chain
FastEthernet0/0 2 2
Loopback1 2 2
Loopback33 2 2
Automatic network summarization is not in effect
Maximum path: 4
Routing for Networks:
1.0.0.0
10.0.0.0
192.168.23.0
Routing Information Sources:
Gateway Distance Last Update
192.168.23.2 120 00:00:22
Distance: (default is 120)
The time timer values apply to
either RIP version 1 or 2.
To lower the values.
R3(config-router)#timers basic 5
20 20 30
This says – change the updates to
5 seconds / invalid to 20 seconds / Hold to 20 seconds and flush to 30 seconds.
Note: if you set the hold down to
0, the route will never go into hold down.
Verification:
R3#sh ip protocols
Routing Protocol is
"rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 5 seconds, next due in 3 seconds
Invalid after 20 seconds, hold down 20, flushed after 30
Note: the timers in RIP are not
100% accurate, the RIP process uses something known as RIP Jitter. Which is basically
a randomization of the timers to make sure the router is not sending or receiving
updates out the interface at the exact same time index. This is why the timers
are large by default.
There is a limit to the packet
format to RIP. So some updated do not make it in each update.
