Building OSPF adjacency

Database Description Packet (DDP) - This contains the summary of all the LSAs, it only contains the headers and not the complete LSA. This allows router to see if its own link state database is updated. This is type 2 OSPF packet. I(nitial)-bit - If set means this is the first DDP sent. M(ore)-bit - … Continue reading Building OSPF adjacency

OSPF finite state machine

Reference: Routing TCP/IP 2nd Edition Jeff Doyle, page 353-357. OSPF router goes through several states before adjacency is formed. DOWN - No hello packets was seen from the neighbour router since the last dead interval. If an OSPF router goes to DOWN state from its higher states, its link state retransmission, database summary and link … Continue reading OSPF finite state machine


R2 hub router interface Serial1/0  no ip address  encapsulation frame-relay  serial restart-delay 0 interface Serial1/0.102 point-to-point  ip address  frame-relay interface-dlci 102 end interface Serial1/0.103 multipoint  ip address  ip ospf priority 10  frame-relay interface-dlci 103  frame-relay interface-dlci 104 end router ospf 1  router-id  log-adjacency-changes  passive-interface default  no passive-interface Serial1/0.102  no passive-interface … Continue reading OSPF over NBMA

Tshoot: A network was not shown in OSPFv3 routing table

Reference topology Refer to IPv6 Layer 3 topology. Reference explanation. While I was doing IPv6 redistribution from ripng to OSPFv3, I found that OSPFv3 routing table did not include the 2026::2:/122 network which is in the RIPng domain between DSW1 and R4. DSW1 however has all the RIPng external routes but cannot ping to 2026::1:/122 … Continue reading Tshoot: A network was not shown in OSPFv3 routing table

OSPF: A note about OSPF authentication

Interface level command ip ospf authentication message-digest (Enable MD5 authentication) ip ospf message-digest-key 1 md5 cisco ip ospf authentication (Enable clear text authentication) ip ospf authentication-key cisco OSPF authentication type Type 0: Null, no authentication Command: ip ospf authentication null Type 1: Clear text Command: ip ospf authentication Type 2: MD5 hash authentication Command: ip … Continue reading OSPF: A note about OSPF authentication

Connecting Enterprise hub to other enterprise spokes over NBMA (frame-relay)

The original design intention is not to advertise routes using ospf over NBMA network, it is not necessary for this case. However for Buona Vista HQ to be able to reach the two sites, I need entries in the routing table to let other routers know the road map to reach. A way is to … Continue reading Connecting Enterprise hub to other enterprise spokes over NBMA (frame-relay)

OSPF: non-broadcast multiaccess (point-to-multipoint type)

RFC2328 compliant (point-to-multipoint type) 1. RFC2328 compliant mode. 2. No DR and BDR is/are needed. 3. Multicast OSPF hello packet is sent to discover neighbours. 4. Typically for partial mesh or star topology.   Debug output of 2651-4 2651-4# *Mar  3 11:26:39.841: OSPF: Interface Serial0/0.301 going Up *Mar  3 11:26:39.841: OSPF: Send hello to … Continue reading OSPF: non-broadcast multiaccess (point-to-multipoint type)

OSPF: non-broadcast multaccess network (broadcast type)

OSPF using broadcast network type over NBMA 1. Uses multicast (, AllSPFRouter multicast) to automatically discover neighbours, no need to use neighbor command for OSPF router to send hello via unicast. 2. Cisco mode. (non RFC2328-compliant) 3. DR and BDR will be elected. 4. Typically full mesh or partial mesh topology. 5. Hello is sent … Continue reading OSPF: non-broadcast multaccess network (broadcast type)