Like OSPF, ISIS uses the Dijkstra algorithm to compute the best paths to destinations within the network.
What are the pros of ISIS?
The most appealing thing about ISIS is that this IGP has ability to support multiple protocols. ISIS can support IPv4 and IPv6 simultaneously. If IPv6 migration isn’t on your mind then you are going to be shocked when the requirements come down from on high in the near future. That means a single IGP for your network instead of two, like OSPFv2 and OSPFv3.
ISIS is very scalable – some would say more scalable than it’s SPF counterpart OSPF. The benefit of ISIS over OSPF is that there is no mandatory backbone area. Essentially, a router belongs to a single specific area. The area boundaries are not determined by the router itself (like an OSPF ABR) but rather the boundary exists on the links that interconnect the areas (between routers). Level 1 interfaces are used for INTRA area communications and level 2 interfaces are used for INTER area communications.
ISIS is highly extensible with its TLV (type, length, value) PDU format. Traffic engineering is turned on by default. If you are looking to deploy MPLS-TE and IPv6 in the near future, you can do it all with ISIS. The fact that TLV 137 dynamically shares the hostname of the routers in the network. The slew of available features on ISIS are extremely refreshing.
What are some cons of ISIS?
ISIS is so close to OSPF, yet very different – that’s why we get ourselves into trouble. ISIS uses course metrics by default. If you have two circuits that are different speeds they will be treated equally – a default interface metric of 10 is used. If still haven’t figured out that you are using the course metrics, the max metric will be set at 63 regardless of the aggregate or configured value. The upside is that wide-metrics are available allowing for a maximum interface value of 16,777,215. Don’t forget to use wide-metrics.
The last con for ISIS is the NET address. Just when you thought you could forget all that useless LANE information, you can now refresh your memory is remembering about the NET address. Essentially, the NET address has several functions so lets break one down.
49.0001.1921.6810.0001.00
Well, theses are pros and cons for ISIS in a nutshell. ISIS protocol has serious potential in the future for Enterprise networks as we migrate to IPv6. Additionally, as more Enterprises deploy MPLS, the idea that a single IGP can support all of your interior gateway functions is appealing. There will be a learning curve, but with all things the more experience you have working with something the more proficient you become.
What are the pros of ISIS?
The most appealing thing about ISIS is that this IGP has ability to support multiple protocols. ISIS can support IPv4 and IPv6 simultaneously. If IPv6 migration isn’t on your mind then you are going to be shocked when the requirements come down from on high in the near future. That means a single IGP for your network instead of two, like OSPFv2 and OSPFv3.
ISIS is very scalable – some would say more scalable than it’s SPF counterpart OSPF. The benefit of ISIS over OSPF is that there is no mandatory backbone area. Essentially, a router belongs to a single specific area. The area boundaries are not determined by the router itself (like an OSPF ABR) but rather the boundary exists on the links that interconnect the areas (between routers). Level 1 interfaces are used for INTRA area communications and level 2 interfaces are used for INTER area communications.
ISIS is highly extensible with its TLV (type, length, value) PDU format. Traffic engineering is turned on by default. If you are looking to deploy MPLS-TE and IPv6 in the near future, you can do it all with ISIS. The fact that TLV 137 dynamically shares the hostname of the routers in the network. The slew of available features on ISIS are extremely refreshing.
What are some cons of ISIS?
ISIS is so close to OSPF, yet very different – that’s why we get ourselves into trouble. ISIS uses course metrics by default. If you have two circuits that are different speeds they will be treated equally – a default interface metric of 10 is used. If still haven’t figured out that you are using the course metrics, the max metric will be set at 63 regardless of the aggregate or configured value. The upside is that wide-metrics are available allowing for a maximum interface value of 16,777,215. Don’t forget to use wide-metrics.
The last con for ISIS is the NET address. Just when you thought you could forget all that useless LANE information, you can now refresh your memory is remembering about the NET address. Essentially, the NET address has several functions so lets break one down.
49.0001.1921.6810.0001.00
- 49.0002 is the Area ID
- 1921.6810.0001 is the system ID (I embedded the IP address 192.168.100.1)
- 00 is the selector byte (keep it 00)
Well, theses are pros and cons for ISIS in a nutshell. ISIS protocol has serious potential in the future for Enterprise networks as we migrate to IPv6. Additionally, as more Enterprises deploy MPLS, the idea that a single IGP can support all of your interior gateway functions is appealing. There will be a learning curve, but with all things the more experience you have working with something the more proficient you become.
No comments:
Post a Comment