Hi, everyone!
Today I’m going to introduce you what is the difference between ISIS vs OSPF. Please see more details in the table below.
ISIS vs OSPF
| ISIS | OSFP | |
| Working layer | ISIS works on data link layer, it can avoid the disadvantages of the IP-based protocol, such as DoS attack and ip packet cheating | OSFP works on network layer, it's an IP-based protocol, IP protocol No.89 |
| Scalability | ISIS packet use TLV format, which makes the ISIS provide a better scalability than OSFP do. routers those enable ISIS can ignore the TLVs which they doesn't support | OSFP packet format can't be extended, but the LSA packet can be extended. those LSA which don't recognized by the neighbor router will not be spread out. |
| ipv6 | ISIS supports ipv6 | OSFP doesn't support ipv6, if we want to run OSFP on ipv6 network enviroment, the OSFPv3 should be enabled |
| Area | ISIS contains two types of area, backbone area and non-backbone area, the routers in the non-backbone area are level 1 router, the routers in the backbone area are level 2 router, the routers which connect the two areas are the level 1/2 router. The backbone area should be connect directly and physically, though the vlink has been defined, but until now, vlink hasn't been realized on the real device. | OSFP contains backbone area, normal area, stub area, totally stub area, nssa area and totally nssa area. the router which connects the backbone area and other area is the ABR, the router which imports the route is the ASBR. Unlike ISIS, vlink has been realized in OSFP, so the backbone area in OSFP can be seperated physically, but they should connect logically. |
| Packet | ISIS contains three types of packets, IIH, LSP and SNP. IIH packet, which is same as hello packet in OSFP, contains level 1 IIH, level 2 IIH and P2P IIH. LSP, which works like LSU packet in OSFP, contains level 1 LSP and level 2LSP. SNP contain CSNP which also divides into level 1 CSNP, level 2 CSNP, and PSNP which contains level 1 PSNP, level 2 PSNP. LSP, which works like LSU packet in OSFP, contains level 1 LSP and level 2 LSP. SNP contain CSNP which also divides into level 1 CSNP, level 2 CSNP, and PSNP which contains level 1 PSNP, level 2 PSNP. | OSFP contains five types of packets, which are hello packet, DBD packet, LSR packet, LSU packet, LSAck packet. |
| Neighbor relationship | Those routers which run the same level ISIS and in the same network segment will establish adjacency relationship with each other. | In the broadcast and NBMA networks, the DRother establish adjacency relationship with DR/BDR, the DRother wouldn't establish adjacncy relationship with other DRother, the state between two DRother will stay at 2-way. |
| DR/DIS | In the broadcast network, DIS which is like DR in OSPF, will be elected, and the DIS can be preempted, when a new router with a higher priority joins into the area, it will preempt the DIS from the current one. | In the broadcast network, DR and BDR will be voted, on the contrary, in P2P and P2MP network don't. |
| Supported network | ISIS supports only the broadcast network and P2P network, besides, the broadcast network can be modified to P2P network. | OSFP supports P2P network, P2MP network, broadcast network and NBMA network. |
| Authentication | ISIS contains three types of authentication, port authentication, area authentication, domain authencation. port authentication will affect the establishing adjacency relationship, area authentication and domain authentication will affect the LSP exchanging. | OSFP authentication only affect establishing adjacency relationship. |
| MTU | When an MTU mismatch, the router wouldn't establish adjacency relationship. | though the MTU will affect the adjacency relationship establishment, but if we ignore the MTU inspection, the mismatched MTU would affect establishing adjacency relationship. |
| import-route | When import route without specifing the level, the route will be import into level 2 by default. This will make none route are imported when importing route on the level 1 router without specifing the level. | Import route is ebabled on the ASBR. |
This would be all on ISIS vs OSPF. Hope this helps!
