CCNP TSHOOT Learning Guide/Chapter 5

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Maintaining and Troubleshooting Routing Solutions


Redistribution metrics
Protocol Default Seed Metric
RIP Infinity
OSPF 20 except from BGP then 1

Redistribute from OSPF to EIGRP


router eigrp 1
 redistribute ospf 100 metric 64 10000 255 1 1500

IOS Commands to verify Routing Functions

Verifying and Troubleshooting Route Propagation

Debug ip routing

R1#<input>debug ip routing</input>
IP routing debugging is on
R1#<input>clear ip eigrp 1 neighbors</input>
Jun 18 12:45:44: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: <notice>Nei (Fa0/1) is down: manually cleared</notice>
Jun 18 12:45:44: RT: delete route to via, eigrp metric [90/28416]
Jun 18 12:45:44: RT: no routes to
Jun 18 12:45:44: RT: NET-RED
<notice>...OUTPUT OMITTED...</notice>
Jun 18 12:45:44: RT: NET-RED
Jun 18 12:45:46: RT: NET-RED
Jun 18 12:45:47: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: <notice>Nei (Fa0/1) is up: new adjacency</notice>
Jun 18 12:45:47: RT: network is now variably masked
Jun 18 12:45:47: RT: add via, eigrp metric [90/28416]
Jun 18 12:45:47: RT: NET-RED
Jun 18 12:45:47: RT: add via, eigrp metric [90/28416]
<notice>...OUTPUT OMITTED...</notice>
Jun 18 12:45:47: RT: add via, eigrp metric [90/158976]
Jun 18 12:45:47: RT: NET-RED
R1#<input>no debug ip routing</input>
IP routing debugging is off

Route Profiling

R1(config)#<input>ip route profile</input>
Jun 18 12:46:41.803: %SYS-5-CONFIG_I: Configured from console by console
R1#<input>sh ip route profile</input>
IP routing table change statistics:
Frequency of changes in a 5 second sampling interval
Change/   Fwd-path  Prefix   Nexthop  Pathcount  Prefix
interval  change    add      change   change     refresh
0         2         2        2        2          1
1         0         0        0        0          1
2         0         0        0        0          0
3         0         0        0        0          0
4         0         0        0        0          0
<notice>...OUTPUT OMITTED...</notice>
3905      0         0        0        0          0
7030      0         0        0        0          0
10155     0         0        0        0          0
13280     0         0        0        0          0
Overflow  0         0        0        0          0
R1#<input>conf t</input>
R1(config)#<input>no ip route profile</input>

show ip cef

SW1#<input>show ip cef exact-route</input> -> => IP adj out of Vlan1, addr



ip access-list extended ISP-CON1
 remark Internally used nets denied. They should be routed by the FIB
 deny   ip
 deny   ip
 permit ip any
ip prefix-list DEFAULT seq 5 permit
route-map HETH permit 5
 match ip address ISP-CON1
 set ip next-hop
route-map HETH permit 10
 match ip address prefix-list DEFAULT
 set ip next-hop

prefix lists

Example Prefix-lists are numbered. In this example "secret net" are not announced.

  • Note: As with access-lists there are an implicit deny in the end.
ip prefix-list SECRET-NET seq 10 deny
ip prefix-list SECRET-NET seq 20 deny
ip prefix-list SECRET-NET seq 30 permit le 32 !Permit all other nets
router bgp 100
  neighbor remote-as 200
  neighbor prefix-list SECRET-NET out

Troubleshooting EIGRP

EIGRP uses three tables

  • interface table:
EIGRP Tables
Table Description
Interface Contains list of all interfaces that have been enabled for processing of EIGRP packets. Passive interfaces are not listed in this table.
Neighbor Keeps track of all active EIGRP neighbors. Neighbours are added on the reception of hello packet and are removed when the hold-time expires or when the associated interface goes down or removed from the Interface table. This table also keeps track on status on Routing information exchanged.
Topology Holds all Routes received from neighbors, locally injected or redistributed into EIGRP. EIGRP selects the best routes from this table based on the DUAL algorithm.

Monitoring EIGRP

show commands

  • show ip eigrp interface
  • show ip eigrp neighbors
  • show ip eigrp topology

debug commands

  • debug ip routing
  • debug eigrp packets - Many options here (terse - except hello packets)
  • debug ip eigrp neighbor as-number network mask
  • debug ip eigrp as-number network mask - limit info. from debug eigrp packets


R1#<input>sh ip protocols</input>
Routing Protocol is "eigrp 1"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
  EIGRP maximum hopcount 100
  EIGRP maximum metric variance 1
  Redistributing: static, eigrp 1
  EIGRP NSF-aware route hold timer is 240s
  Automatic network summarization is not in effect
  Maximum path: 4
  Routing for Networks:
  Passive Interface(s):
  Passive Interface(s):
  Routing Information Sources:
    Gateway         Distance      Last Update              90      00:07:33
  Distance: internal 90 external 170

Many options debugging eigrp

  R1#<input>debug eigrp packets ?</input>
  SIAquery  EIGRP SIA-Query packets
  SIAreply  EIGRP SIA-Reply packets
  ack       EIGRP ack packets
  hello     EIGRP hello packets
  ipxsap    EIGRP ipxsap packets
  probe     EIGRP probe packets
  query     EIGRP query packets
  reply     EIGRP reply packets
  request   EIGRP request packets
  retry     EIGRP retransmissions
  stub      EIGRP stub packets
  terse     Display all EIGRP packets except Hellos
  update    EIGRP update packets
  verbose   Display all EIGRP packets

Troubleshooting OSPF

OSPF tables
Table Description
Interface table List all interfaces enabled for OSPF. The directly connected subnets are included in the TYPE-1 Router LSA the Router injects into the OSPF link-state database. Passive-interfaces are listed in the tables
Neighbor table Used to keep track of all OSPF neighbors. Neighbors are added on the reception of a hello packet and removed when the dead-time expires or when the associated interface goes down.
Link State database Main data structure containing all network topology information for the OSPF process.
Routing Information Base Contains results from the SPF algorithm. OSPF offers the contents of the RIB to the Routing Table.

Neighbor states

OSPF Neighbor states
State Description
Attempt This state is only valid for manually configured neighbors in an NBMA environment. In Attempt state, the router sends unicast hello packets every poll interval to the neighbor, from which hellos have not been received within the dead interval.
Init This state specifies that the router has received a hello packet from its neighbor, but the receiving router's ID was not included in the hello packet. When a router receives a hello packet from a neighbor, it should list the sender's router ID in its hello packet as an acknowledgment that it received a valid hello packet.
2-Way This state designates that bi-directional communication has been established between two routers. Bi-directional means that each router has seen the other's hello packet. This state is attained when the router receiving the hello packet sees its own Router ID within the received hello packet's neighbor field. At this state, a router decides whether to become adjacent with this neighbor. On broadcast media and non-broadcast multiaccess networks, a router becomes full only with the designated router (DR) and the backup designated router (BDR); it stays in the 2-way state with all other neighbors. On Point-to-point and Point-to-multipoint networks, a router becomes full with all connected routers.

At the end of this stage, the DR and BDR for broadcast and non-broadcast multiacess networks are elected. For more information on the DR election process, refer to DR Election.

Note: Receiving a Database Descriptor (DBD) packet from a neighbor in the init state will also a cause a transition to 2-way state.

Exstart Once the DR and BDR are elected, the actual process of exchanging link state information can start between the routers and their DR and BDR.

In this state, the routers and their DR and BDR establish a master-slave relationship and choose the initial sequence number for adjacency formation. The router with the higher router ID becomes the master and starts the exchange, and as such, is the only router that can increment the sequence number. Note that one would logically conclude that the DR/BDR with the highest router ID will become the master during this process of master-slave relation. Remember that the DR/BDR election might be purely by virtue of a higher priority configured on the router instead of highest router ID. Thus, it is possible that a DR plays the role of slave. And also note that master/slave election is on a per-neighbor basis.

Exchange In the exchange state, OSPF routers exchange database descriptor (DBD) packets. Database descriptors contain link-state advertisement (LSA) headers only and describe the contents of the entire link-state database. Each DBD packet has a sequence number which can be incremented only by master which is explicitly acknowledged by slave. Routers also send link-state request packets and link-state update packets (which contain the entire LSA) in this state. The contents of the DBD received are compared to the information contained in the routers link-state database to check if new or more current link-state information is available with the neighbor.
Loading In this state, the actual exchange of link state information occurs. Based on the information provided by the DBDs, routers send link-state request packets. The neighbor then provides the requested link-state information in link-state update packets. During the adjacency, if a router receives an outdated or missing LSA, it requests that LSA by sending a link-state request packet. All link-state update packets are acknowledged.
Full In this state, routers are fully adjacent with each other. All the router and network LSAs are exchanged and the routers' databases are fully synchronized.

Full is the normal state for an OSPF router. If a router is stuck in another state, it's an indication that there are problems in forming adjacencies. The only exception to this is the 2-way state, which is normal in a broadcast network. Routers achieve the full state with their DR and BDR only. Neighbors always see each other as 2-way.

INSERT TABLE 5.2 and FIGURE 5.3 from page 168

Cisco IOS OSPF commands

Show commands

  • show ip ospf interface
  • show ip ospf neighbor
  • show ip ospf datatbase
  • show ip ospf statistics

debug commands

  • debug ip routing
  • debug ip ospf packet
  • debug ip ospf adj
  • debug ip ospf monitor

Troubleshooting BGP

BGP has two maintables

BGP Tables
Table Description
Neighbor table List all neighbors configured on the router. Contains AS, state, time up/down, and how many prefixes exchanged
BGP table Also called BGP RIB stores all locally injected routes and all routes received from neighbors/peers and routing info such as Nexthop, AS, MED, metric origin etc.

Troubleshooting commands

show commands

  • show ip bgp summary
  • show ip bgp neighbors [ip-address]
  • show ip bgp [prefix]

debug commands

  • debug ip bgp
  • debug ip bgp updates