Lab1 Network Issues

• Our first lab network uses RIP v1, has 24 routers arranged in a circular topology

• RIP’s maximum diameter is 15, so parts of the network may be unreachable, especially the RIP annoucement for default

• Added an additional ethernet link on R10 into VLAN61 to resolve by reducing network “diameter”

baselab24.vsd 18-Jan-2005 R.Curci

VLAN10E1

R10

R11

E1VLAN20

E1

R20

R21

E1VLAN30

E1

R30

R31

E1VLAN50

E1

R50

R51

E1VLAN40

E1

R40

R41

E1VLAN60

E1

R60

R61

E1

VLAN120E1

R120

R121

E1VLAN110

E1

R110

R111

E1VLAN100

E1

R100

R101

E1VLAN80

E1

R80

R81

E1VLAN90

E1

R90

R91

E1VLAN70

E1

R70

R71

E1

VLAN11 VLAN31 VLAN51

E0E0

VLAN21 VLAN41

VLAN71VLAN91

VLAN101VLAN81

VLAN111

VLA

N121

VLA

N61

E0

E0E0

E0E0E0E0

E0

E0 E0

R6/FWR1

COMPUTERSCIENCE

SERVER

E0

E0E0

E0

E0

E0

E0

E0

E0

E0E0

E0

Basic 24-Node ITL Lab(extra link added to reduce RIP diameter <16)

IP ADRESS NOTES:Use IP addresses of the form 192.168.X.Y/24unless otherwise noted.Set third octet X to VLAN number.Set last octet Y to router number.

VLAN61

RIP v1– Routing Information Protocol• RIP Versions

– RIP v1 (original version, Doyle ch 5)– RIP v2 (improved version, Doyle ch 7)

• Simple distance-vector protocol (aka Bellman-Ford algorithm)

• Use hop count metric to determine best path (does not take other factors into account such as link speed)

• Initially popular because “routed” implementation bundled with BSD UNIX

• Original IP version adapted for other network protocols such as Novell IPX

RIP – Message Format

• Two Message Types– Request (sent by devices after initialization to request a

unicast copy of a neighbor’s routing table

– Response (sent by RIP speaking devices by broadcasting every 30 seconds to IP 255.255.255.255)

• Send via UDP/520 up to 25 routes per packet that include IP network, metric, but no subnet mask

RIP – Normal Operation

• For every active RIP interface– Announce known RIP routes out RIP enabled interfaces

every 30s

– Process received RIP annoucements by placing routes in routing table if better than existing route and add 1 to the hop count

– Do not announce things learned on an interface out the same interface (split horizon)

– Only announce if reachable with hop count <- 15

RIP Timers (Cisco Imp.)

Router rip timers basic update invalid holddown flush• Update 30s (when to broadcast response)• Invalid 180s (when haven’t heard annoucements

for 180s, do not use)• Holddown 180s (when neighbor increases metric

for a network, do not accept immediately• Flush 240s (after invalid timer expires, mark as

unreachable metric 16 until time to flush)

Cisco Administrative Distance

• Routers can run multiple routing protocols simultaneously

• Q: What to do when you have more than one route for a network learned with different routing protocols?

• A: Believe route with smallest administative distance

• For example, RIP uses admin distance 120, static uses 1, so static routes are more “believable”

RIP v2 improvements

• Will cover these later in Doyle ch 7• Annoucements carry subnet masks

therefore supporting classful routing• Subnets of classful nets do not need to all

be the same size, but can be variable length (VLSM)

• Supports IP multicast on 224.0.0.9• Supports MD5 authentication

Cisco RIP commands

• Show ip protocols

• Show ip route

• Show ip route RIP

• Show ip RIP database

• Debug ip RIP

• Debug ip RIP events

• Debug ip routing

Sh ip protocolsR10#sh ip protocolsRouting Protocol is "rip" Sending updates every 30 seconds, next due in 14 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Triggered RIP Key-chain Ethernet0/0 1 1 2 Ethernet0/0.11 1 1 2 Ethernet0/0.61 1 1 2 Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 192.168.10.0 192.168.11.0 192.168.61.0 Routing Information Sources: Gateway Distance Last Update 192.168.61.70 120 00:00:18 192.168.10.1 120 00:00:13 192.168.61.61 120 00:00:04 192.168.10.11 120 00:00:16 Gateway Distance Last Update 192.168.11.20 120 00:00:16 Distance: (default is 120)

Sh ip routeR10#sh ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route

Gateway of last resort is 192.168.10.1 to network 0.0.0.0

R 192.168.91.0/24 [120/7] via 192.168.10.11, 00:00:25, Ethernet0/0R 192.168.121.0/24 [120/1] via 192.168.10.11, 00:00:25, Ethernet0/0

R 192.168.31.0/24 [120/4] via 192.168.11.20, 00:00:23, Ethernet0/0.11

C 192.168.61.0/24 is directly connected, Ethernet0/0.61R 192.168.90.0/24 [120/5] via 192.168.61.70, 00:00:02, Ethernet0/0.61R 192.168.120.0/24 [120/2] via 192.168.10.11, 00:00:25, Ethernet0/0R 192.168.30.0/24 [120/3] via 192.168.11.20, 00:00:23, Ethernet0/0.11R 192.168.60.0/24 [120/1] via 192.168.61.61, 00:00:14, Ethernet0/0.61R 192.168.110.0/24 [120/4] via 192.168.10.11, 00:00:25, Ethernet0/0R 192.168.111.0/24 [120/3] via 192.168.10.11, 00:00:25, Ethernet0/0C 192.168.10.0/24 is directly connected, Ethernet0/0R 192.168.40.0/24 [120/5] via 192.168.61.61, 00:00:14, Ethernet0/0.61 [120/5] via 192.168.11.20, 00:00:23, Ethernet0/0.11

Debug ip routing

R10# term monitor

R10# debug ip routing

(plug in ethernet cable here)

R10(config)#int e0/0.61

R10(config-subif)#no shut

R10(config-subif)#

.Jan 20 17:00:12 EST: is_up: 1 state: 4 sub state: 1 line: 1

.Jan 20 17:00:12 EST: RT: closer admin distance for 192.168.61.0, flushing 1 routes

.Jan 20 17:00:12 EST: RT: add 192.168.61.0/24 via 0.0.0.0, connected metric [0/0]

.Jan 20 17:00:12 EST: RT: interface Ethernet0/0.61 added to routing table

.Jan 20 17:00:12 EST: RT: add 192.168.40.0/24 via 192.168.61.61, rip metric [120/5]

SNMP tools to troubleshoot RIP

• Assuming you are on a LINUX computer with “snmpwalk” and “snmpnetstat” tools and your router has a Read-Only community configured named “public”

• ( snmp-server community public RO )• Linux% snmpnetstat –r 192.168.30.30 public• Linux% snmpwalk –v 1 –c public 192.168.30.30

More tools to debug RIP

• Use a sniffer like program such as Ethereal to “sniff” the UDP/520 RIP packets on an ethernet segment with RIP speakers

• Can also use older tools like TCPDUMP but newer tools like Ethereal have better decoding

Lab2 Notes

• We will start a new lab next week with a new topology, subnetting, and more complex RIP configuration

• Will leave topology unchanged for now at least until first assignment due this Friday 1/21/05 7pm ET