Wednesday, September 21, 2011

The Impact of the 'clear ip route' Privileged Command


Below shows the routing table on RT1:
RT1#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 3 subnets
R       172.16.1.0 [120/1] via 10.10.10.2, 00:00:16, FastEthernet0/0
D       172.16.2.0 [90/284160] via 10.10.10.2, 00:02:06, FastEthernet0/0
O       172.16.3.0 [110/11] via 10.10.10.2, 00:01:14, FastEthernet0/0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, FastEthernet0/0
RT1#
RT1#sh ip route summary
IP routing table name is Default-IP-Routing-Table(0)
Route Source    Networks    Subnets     Overhead    Memory (bytes)
connected       0           1           64          152
static          0           0           0           0
eigrp 100       0           1           64          152
ospf 100        0           1           64          152
  Intra-area: 1 Inter-area: 0 External-1: 0 External-2: 0
  NSSA External-1: 0 NSSA External-2: 0
rip             0           1           64          152
internal        2                                   2344
Total           2           4           256         2952
RT1#

Below shows the impact of clearing the RIPv2 route – 172.16.1.0/24. Packet drops were observed.
RT1#debug ip rip
RIP protocol debugging is on
RT1#
RT1#debug ip routing
IP routing debugging is on
RT1#
RT1#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 3 subnets
R       172.16.1.0 [120/1] via 10.10.10.2, 00:00:02, FastEthernet0/0
D       172.16.2.0 [90/284160] via 10.10.10.2, 00:02:51, FastEthernet0/0
O       172.16.3.0 [110/11] via 10.10.10.2, 00:01:59, FastEthernet0/0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, FastEthernet0/0
RT1#
RT1#sh ip rip database
10.0.0.0/8    auto-summary
10.10.10.0/24    directly connected, FastEthernet0/0
172.16.0.0/16    auto-summary
172.16.1.0/24
    [1] via 10.10.10.2, 00:00:03, FastEthernet0/0
RT1#
RT1#clear ip route 172.16.1.0 255.255.255.0
RT1#
RT1#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 2 subnets
D       172.16.2.0 [90/284160] via 10.10.10.2, 00:03:00, FastEthernet0/0
O       172.16.3.0 [110/11] via 10.10.10.2, 00:02:08, FastEthernet0/0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, FastEthernet0/0
RT1#
RT1#sh ip rip database
10.0.0.0/8    auto-summary
10.10.10.0/24    directly connected, FastEthernet0/0
172.16.0.0/16    auto-summary
172.16.1.0/24
    [1] via 10.10.10.2, 00:00:12, FastEthernet0/0
RT1#
00:03:07: RT: del 172.16.1.0/24 via 10.10.10.2, rip metric [120/1]
00:03:07: RT: delete subnet route to 172.16.1.0/24
00:03:07: RT: NET-RED 172.16.1.0/24
00:03:24: RIP: received v2 update from 10.10.10.2 on FastEthernet0/0
00:03:24:      172.16.1.0/24 via 0.0.0.0 in 1 hops
00:03:24: RT: add 172.16.1.0/24 via 10.10.10.2, rip metric [120/1]
00:03:24: RT: NET-RED 172.16.1.0/24
00:03:24:      172.16.2.0/24 via 0.0.0.0 in 1 hops
00:03:24:      172.16.3.0/24 via 0.0.0.0 in 1 hops
RT1#
======================================================================
RT2#ping 10.10.10.1 source 172.16.1.1 repeat 500

Type escape sequence to abort.
Sending 500, 100-byte ICMP Echos to 10.10.10.1, timeout is 2 seconds:
Packet sent with a source address of 172.16.1.1
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.........!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!
Success rate is 98 percent (491/500), round-trip min/avg/max = 4/18/80 ms
RT2#

Below shows the impact of clearing the EIGRP route – 172.16.2.0/24. No packet drop was observed.
RT1#debug ip eigrp
IP-EIGRP Route Events debugging is on
RT1#
RT1#debug ip routing
IP routing debugging is on
RT1#
RT1#sh ip route
======================================================================
RT2#ping 10.10.10.1 source 172.16.2.1 repeat 500

Type escape sequence to abort.
Sending 500, 100-byte ICMP Echos to 10.10.10.1, timeout is 2 seconds:
Packet sent with a source address of 172.16.2.1
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!
Success rate is 100 percent (500/500), round-trip min/avg/max = 4/17/72 ms
RT2#


Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 3 subnets
R       172.16.1.0 [120/1] via 10.10.10.2, 00:00:24, FastEthernet0/0
D       172.16.2.0 [90/284160] via 10.10.10.2, 00:05:03, FastEthernet0/0
O       172.16.3.0 [110/11] via 10.10.10.2, 00:04:11, FastEthernet0/0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, FastEthernet0/0
RT1#
RT1#sh ip eigrp neighbors
IP-EIGRP neighbors for process 100
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                            (sec)         (ms)       Cnt Num
0   10.10.10.2              Fa0/0             12 00:05:06   20   200  0  1
RT1#
RT1#sh ip eigrp topology
IP-EIGRP Topology Table for AS(100)/ID(10.10.10.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 10.10.10.0/24, 1 successors, FD is 28160
        via Connected, FastEthernet0/0
P 172.16.2.0/24, 1 successors, FD is 284160
        via 10.10.10.2 (284160/281600), FastEthernet0/0
RT1#
RT1#clear ip route 172.16.2.0 255.255.255.0
RT1#
RT1#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 3 subnets
R       172.16.1.0 [120/1] via 10.10.10.2, 00:00:14, FastEthernet0/0
D       172.16.2.0 [90/284160] via 10.10.10.2, 00:00:00, FastEthernet0/0
O       172.16.3.0 [110/11] via 10.10.10.2, 00:04:28, FastEthernet0/0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, FastEthernet0/0
RT1#
00:05:27: RT: del 172.16.2.0/24 via 10.10.10.2, eigrp metric [90/284160]
00:05:27: RT: delete subnet route to 172.16.2.0/24
00:05:27: RT: NET-RED 172.16.2.0/24
00:05:27: RT: add 172.16.2.0/24 via 10.10.10.2, eigrp metric [90/284160]
00:05:27: RT: NET-RED 172.16.2.0/24
RT1#

Below shows the impact of clearing the OSPF route – 172.16.3.0/24. No packet drop was observed.
RT1#debug ip ospf events
OSPF events debugging is on
RT1#
RT1#debug ip routing
IP routing debugging is on
RT1#
RT1#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 3 subnets
R       172.16.1.0 [120/1] via 10.10.10.2, 00:00:05, FastEthernet0/0
D       172.16.2.0 [90/284160] via 10.10.10.2, 00:01:17, FastEthernet0/0
O       172.16.3.0 [110/11] via 10.10.10.2, 00:05:45, FastEthernet0/0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, FastEthernet0/0
RT1#
RT1#sh ip ospf neighbor

Neighbor ID     Pri   State         Dead Time   Address      Interface
172.16.3.1        1   FULL/DR       00:00:39    10.10.10.2   FastEthernet0/0
RT1#
RT1#sh ip ospf database

            OSPF Router with ID (10.10.10.1) (Process ID 100)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
10.10.10.1      10.10.10.1      360         0x80000002 0x00FBB8 1
172.16.3.1      172.16.3.1      360         0x80000002 0x009105 2

                Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
10.10.10.2      172.16.3.1      361         0x80000001 0x004A2F
RT1#
RT1#clear ip route 172.16.3.0 255.255.255.0
RT1#
RT1#sh ip route

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 3 subnets
R       172.16.1.0 [120/1] via 10.10.10.2, 00:00:19, FastEthernet0/0
D       172.16.2.0 [90/284160] via 10.10.10.2, 00:01:31, FastEthernet0/0
O       172.16.3.0 [110/11] via 10.10.10.2, 00:00:00, FastEthernet0/0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, FastEthernet0/0
RT1#
00:06:58: RT: del 172.16.3.0/24 via 10.10.10.2, ospf metric [110/11]
00:06:58: RT: delete subnet route to 172.16.3.0/24
00:06:58: RT: NET-RED 172.16.3.0/24
00:06:59: RT: add 172.16.3.0/24 via 10.10.10.2, ospf metric [110/11]
00:06:59: RT: NET-RED 172.16.3.0/24
RT1#
RT1#sh ip ospf database

            OSPF Router with ID (10.10.10.1) (Process ID 100)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
10.10.10.1      10.10.10.1      380         0x80000002 0x00FBB8 1
172.16.3.1      172.16.3.1      380         0x80000002 0x009105 2

                Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
10.10.10.2      172.16.3.1      381         0x80000001 0x004A2F
RT1#
======================================================================
RT2#ping 10.10.10.1 source 172.16.3.1 repeat 500

Type escape sequence to abort.
Sending 500, 100-byte ICMP Echos to 10.10.10.1, timeout is 2 seconds:
Packet sent with a source address of 172.16.3.1
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!
Success rate is 100 percent (500/500), round-trip min/avg/max = 4/20/76 ms
RT2#

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