Vsys of Isis (virtual system)

First of all, you need to know ISIS The virtual system of is used to partition .

1. What then? ISIS Need to slice , and OSPF No need to ？

because OSPF Is based on IP layer , Layer 3 already provides slicing , therefore OSPF There is no need to support slicing . however ISIS It is based on two layers , Layer 2 does not support slicing , therefore ISIS A slicing function must be provided separately . But one ISIS The maximum number of slices supported by the device is 256 individual , If it exceeds the limit, you cannot continue to send in pieces .

2. The problem is coming. , If for a big one LSDB The data needs to be transmitted ,256 One slice is not enough , How to solve it ？

It's time to ISIS Of vsys（virtual system） Come and solve

ISIS Of vsys Two modes are supported ：

        ①mode1（ Compatibility mode ）：

                 Applicable scenario ： stay ISIS In the network , Some devices do not support vsys

                Working mode ： At this time vsys It will work in the working mode of real equipment , But pay attention to local devices （ To configure vsys The equipment ） arrive vsys Of that logical link cost by max-1, It's a local device ---->vsys, The middle virtual link goes to vsys In this direction cost=max-1, and vsys----> Local device ,cost by 0. Why is it designed like this ？ because vsys The purpose of is to send the route in pieces , Instead of calculating routes , Because in compatibility mode vsys It works as a real device , So you have to set cost by max-1, In this way, you only need to go through any link ,cost will =max, such vsys You won't learn routing . however ,vsys----> Local device ,cost=0, That means ,vsys Route sent out ,cost Will keep the real device cost, Configuration vsys The reality of the device that functions top Of cost.

        ②mode2（ Full mode ）：

                 Applicable scenario ： stay ISIS In the network , All devices support vsys function

                 Working mode ： adopt type=24 Of TLV Encapsulate route issue , Other equipment will receive this later LSP, Check out type=2

4 Of TLV Routing information for , This routing information will be regarded as configuring this vsys Real devices for （ Initial equipment ） Sent out , Realize fragmentation function