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How do I troubleshoot an OSPF link stuck in EXST/EXCH state?

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TitleHow do I troubleshoot an OSPF link stuck in EXST/EXCH state?
Question
OSPF enabled on the router neighbor interfaces.
NetIron XMR / MLX / MLXe / CES / CER platforms.
All software releases.

Router1----------L2 switch----------Router2
1/11/1
10.0.0.1/3010.0.0.2/30
OSPF area 0 OSPF area 0
Environment
Answer
1. Verify OSPF state between Router1 and Router2.
Show ip ospf neighbor
Example:
telnet@Router1# show ip ospf neighbor
Number of Neighbors is 1, in FULL state 0
Port Address Pri State Neigh Address Neigh ID Ev Opt Cnt
1/110.0.0.1 1 EXST/DR10.0.0.2 2.2.2.2 12 660
telnet@Router1#
2. Verify connectivity between Router1 and Router2 by pinging from Router1 to Router2.
Ping 10.0.0.2 count 5
Example:
telnet@Router1 # ping 10.0.0.2 count 5
Sending 5, 16-byte ICMP Echo to 10.0.0.2, timeout 5000 msec, TTL 64
Type Control-c to abort
Reply from 10.0.0.2: bytes=16 time=1ms TTL=64
Reply from 10.0.0.2: bytes=16 time<1ms TTL=64
Reply from 10.0.0.2: bytes=16 time<1ms TTL=64
Reply from 10.0.0.2: bytes=16 time<1ms TTL=64
Reply from 10.0.0.2: bytes=16 time<1ms TTL=64
Success rate is 100 percent (5/5), round-trip min/avg/max=0/0/1 ms.
telnet@Router1 #
3. Verify default-max-frame-size and interface IP MTU are configured consistently along the L2 path between Router1 and Router2.
Show interface <interface-id> #check the default-max-frame-size of the interface
Example:
telnet@Router1 # show interface ethernet 1/1
GigabitEthernet1/1 is up, line protocol is up
STP Root Guard is disabled, STP BPDU Guard is disabled
Hardware is GigabitEthernet, address is 748e.f83c.8c56 (bia 748e.f83c.8c56)
Configured speed auto, actual 1Gbit, configured duplex fdx, actual fdx
Member of Control VLAN 4095, VLAN 1 (untagged), port is in untagged mode, port state is Forwarding
STP configured to ON, Priority is level0, flow control enabled
Priority force disabled, Drop precedence level 0, Drop precedence force disabled
dhcp-snooping-trust configured to OFF
mirror disabled, monitor disabled
LACP BPDU Forwarding:Disabled
LLDP BPDU Forwarding:Disabled
Not member of any active trunks
Not member of any configured trunks
No port name
Port is not enabled to receive all vlan packets for pbr
Internet address is 10.0.0.1/30, MTU 9216 bytes, encapsulation ethernet
Port-type: default-port
Cluster L2 protocol forwarding enabled
300 second input rate: 211 bits/sec, 0 packets/sec, 0.00% utilization
300 second output rate: 469 bits/sec, 0 packets/sec, 0.00% utilization
104430 packets input, 19914970 bytes, 0 no buffer
Received 2707 broadcasts, 98891 multicasts, 2832 unicasts
0 input errors, 0 CRC, 0 frame, 0 ignored
0 runts, 0 giants
NP received 0 packets, Sent to TM 1 packets
NP Ingress dropped 2 packets
544648 packets output, 48616944 bytes, 0 underruns
Transmitted 2710 broadcasts, 507013 multicasts, 34925 unicasts
0 output errors, 0 collisions
NP transmitted 3 packets, Received from TM 4 packets
telnet@Router1#
Show ip interface <interface-id> #check the IP MTU of the interface
Example:
telnet@Router1 # show ip interface ethernet 1/1
Interface Ethernet 1/1 (0)
port enabled
port state: UP
ip address: 10.0.0.1/30
Port belongs to VRF: default-vrf
encapsulation: ETHERNET, mtu: 1526
MAC Address 748e.f83c.8c56
directed-broadcast-forwarding: disabled
ip icmp redirect: enabled
ip local proxy arp: disabled
ip ignore gratuitous arp: disabled
No inbound ip access-list is set
No outbound ip access-list is set
No Helper Addresses are configured.
RPF mode: NoneRPF Log: Disabled
0 unicast RPF drop
ignore-options: Disabled
RxPkts: 0 TxPkts: 0
RxBytes: 0 TxBytes:0
telnet@Router1 #
NOTE: The maximum value of an IP MTU cannot exceed the configured maximum frame size, minus 18.The 18 bytes is used for IP overhead, VLAN tagging, etc.
IP MTU <= default-max-frame-size 18 bytes
If inconsistencies are found, reconfigure the default-max-frame-size and IP MTU as required on the affected device(s) and interface(s), respectively, along the L2 path between Router1 and Router2.
default-max-frame-size <bytes>#default value is 1548 bytes.
ip mtu <bytes> #default value for Ethernet II packets is 1500 bytes.
NOTE: You must run the write memory command and reload the Brocade device for the default-max-frame-size command to take effect.
4. Disable/enable the interface to restart ospf on the link.
Example:
telnet@Router1# conf t
telnet@Router1(config)# int e 1/1
telnet@Router1(config-if-e1000-1/1)# disable
telnet@Router1(config-if-e1000-1/1)# enable
telnet@Router1(config-if-e1000-1/1)#
5. Ping from Router1 to Router2 using packet sizes ranging from 16 bytes to 9170 bytes (if default-max-frame-size 9216 is configured on Router1, L2 switch, and Router2).
Ping 10.0.0.2 count 5 size <bytes>
If the default-max-frame-size and interface IP MTU are configured consistently along the L2 path between Router1 and Router2, all ping packets in this range should go through.
Example:
telnet@Router1# ping 10.0.0.2 count 5 size 9170
Sending 5, 9170-byte ICMP Echo to 10.0.0.2, timeout 5000 msec, TTL 64
Type Control-c to abort
Reply from 10.0.0.2: bytes=9170 time=2ms TTL=64
Reply from 10.0.0.2: bytes=9170 time=2ms TTL=64
Reply from 10.0.0.2: bytes=9170 time=2ms TTL=64
Reply from 10.0.0.2: bytes=9170 time=3ms TTL=64
Reply from 10.0.0.2: bytes=9170 time=2ms TTL=64
Success rate is 100 percent (5/5), round-trip min/avg/max=2/2/3 ms.
telnet@Router1#
6. Verify OSPF state between Router1 and Router2:
Show ip ospf neighbor
Example:
telnet@Router1# show ip ospf neighbor
Number of Neighbors is 1, in FULL state 1
Port Address Pri State Neigh Address Neigh ID Ev Opt Cnt
1/1 10.0.0.11 FULL/DR10.0.0.2 2.2.2.2 12 660
telnet@Router1#
Additional notes

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