MAXHOPS

Name

MAXHOPS -- Set Hopcount Horizon.

Synopsis

MAXHOPS=n (n = 0-30)

Availability

Used only in XROUTER.CFG.

Description

MAXHOPS is a global and PORT configuration keyword used in XROUTER.CFG, and a parameter which can be used in a ROUTE ADD command.

It defines the maximum accepted hop count for new nodes table entries received via INP3 unicasts from neighbours. Node information with hop counts that exceed this figure are not accepted into the nodes table. This parameter has no effect on data received via conventional NetRom nodes broadcasts.

MAXHOPS would typically be used to limit the "hop horizon" to a smaller value than the default horizon, which is 30. Like MAXTT, it can be used to limit the number of node entries that are accepted via a particular port or neighbour.

For example, the RF purists don't like Internet-routed nodes cluttering up their tables, nor do they want traffic to "short-circuit" the RF links via tortuous multi-hop Internet routes. In this case, a low MAXHOPS might be used at the interface between the RF-based network segment and the Internet-based segment, to (a) control the number of Internet nodes appearing in the nodes tables of the RF routers, and (b) limit the run-length of Internet routes.

MAXHOPS can be used in 3 places: If used in the "global" section of XROUTER.CFG, it specifies a default value for all ports, overriding the default of 30. If used in a PORT configuration block, it overrides the global default. All new routes inherit this value. Finally a MAXHOPS value (without the keyword) can be used in a ROUTE ADD entry, to override the PORT default. For example:

	route add g8pzt 5 100 ! 0 0 0 2000 5

This adds a locked in route to neighbour "g8pzt" on port 5, quality 100, with default maxframe, paclen and frack, MAXTT of 2000 and MAXHOPS of 5.

Setting MAXHOPS to 0 will block all received INP3 data.

Caveats

Using MAXHOPS to limit the no. of nodes learned via a neighbour may fail if the neighbour duplicates the INP3 data in NetRom nodes broadcasts. This may enter nodes which are beyond your chosen hop limit into the nodes table and keep them refreshed. The only defence is to ignore data from NetRom broadcasts by setting the port QUALITY below MINQUAL, or to set the MINQUAL high. Both actions may cause the loss of some NetRom-only nodes from the table.

See also

INP3(9) -- InterNode Protocol
MAXTT(7) -- Maximum Trip Time.
MINQUAL(2) -- Display / Set port Minimum Quality
QUALITY(2) -- Display / Modify NetRom Quality.
ROUTES(2) -- Display / Modify NetRom Neighbour Routes.
XROUTER.CFG(8) -- Main Configuration File.