The dynamic hostname exchange mechanism provides a mapping from the hostname to system ID for IS-IS routers.
On an IS-IS router without hostname exchange, information about IS-IS neighbors and LSDBs is represented by a system ID with 12 hexadecimal numbers, for example, aaaa.eeee.1234. This representation is complicated and not easy to use.
To easily maintain and manage IS-IS networks easily, the dynamic hostname exchange mechanism was introduced.
Dynamic hostname information is advertised in the form of a dynamic hostname TLV (type 137) in LSPs. The dynamic hostname exchange mechanism also provides a service to associate a host name with the Designated IS (DIS) on a broadcast network. Then, this mechanism advertises this association through LSPs in the form of a dynamic hostname TLV.
In the implementation of FW, routers with IS-IS dynamic hostname mapping enabled add the Dynamic Hostname TLV (TLV type 137) that records the local host name to the LSPs they generate before sending out the LSPs.
Dynamic Hostname TLV (TLV type 137) includes the following fields:
Type: indicates the dynamic hostname exchange mechanism.
Length: indicates the total length of the value field.
Value: indicates a character string of 1 to 255 characters.
The Dynamic Hostname TLV is optional and can be inserted anywhere in an LSP. The hostname value cannot be null. A router determines whether to carry the TLV in LSPs it sends. The router that receives the LSPs determines whether to ignore the TLV or obtain the TLV for its mapping table.
Matching rules
The dynamic hostname mechanism abides by the longest match rule. First, System ID+NSEL is first compared. If that does not match, the system ID is then compared.
Transmission of dynamic hostname
The dynamic hostname can be carried by the original LSP only.
Transmission of DIS dynamic hostname
The DIS dynamic hostname is transmitted through the LSPs generated by the DIS.
Priority of dynamic hostname
The dynamic hostname takes precedence over the static hostname. When both a dynamic hostname and a static hostname are configured, the dynamic hostname replaces the static hostname.
Configuration and resolution of dynamic hostname
The dynamic hostname can be up to 64 bytes in length and a maximum of 255-byte contents can be resolved.
In maintenance and management, the hostname is easier to identify and retain than the system ID. After this function is configured, the hostname instead of the system ID is displayed when you view information about IS-IS on the router.
The hostname exchange mechanism implemented on the FW includes dynamic hostname mapping and static hostname mapping. The system ID is replaced by the hostname in the following cases:
When an IS-IS neighbor is displayed, the system ID of the IS-IS neighbor is replaced by the dynamic hostname. If the IS-IS neighbor is the DIS, then the system ID of the DIS is replaced by the dynamic hostname of the neighbor.
When an LSP in the IS-IS LSDB is displayed, the system ID in the LSP ID is replaced by the dynamic hostname of the router that advertises the LSP.
When details about the IS-IS LSDB are displayed, the Host Name field is included for the LSP generated by the router where dynamic hostname exchange is enabled; the system ID is replaced by the dynamic hostname of the IS-IS neighbor.