|-c config_file |
| || Specify an alternative file for configuration commands. Default is /etc/mrouted.conf. |
|-d [debug_level] |
| || If no -d option is given, or if the debug level is specified as 0, mrouted detaches from the invoking terminal. Otherwise, it remains attached to the invoking terminal and responsive to signals from that terminal. Regardless of the debug level, mrouted always writes warning and error messages to the system log daemon. The -debug-level argument is a comma-separated list of any of the following: |
| "packet" |
| || Display the type, source and destination of all packets sent or received. |
| "pruning" |
| || Display more information about prunes sent or received. |
| "routing" |
| || Display more information about routing update packets sent or received. |
| "route_detail" |
| || Display routing updates in excruciating detail. This is generally way too much information. |
| "neighbors" |
| || Display information about neighbor discovery. |
| "cache" |
| || Display insertions, deletions and refreshes of entries in the kernel forwarding cache. |
| "timeout" |
| || Debug timeouts and periodic processes. |
| "interface" |
| || Display information about interfaces and their configuration. |
| "membership" |
| || Display information about group memberships on physical interfaces. |
| "traceroute" |
| || Display information about multicast traceroute requests passing through this router. |
| "igmp" || Display IGMP operation including group membership and querier election. |
| "icmp" || Monitor ICMP handling. |
| "rsrr" || Monitor RSRR operation. |
| cache_lifetime secs |
| || Specifies, in seconds, the lifetime of a multicast forwarding cache entry in the kernel. Multicast forwarding cache entries in the kernel are checked every secs seconds, and are refreshed if the source is still active or deleted if not. Care should be taken when setting this value, as a low value can keep the kernel cache small at the cost of "thrashing" the cache for periodic senders, but high values can cause the kernel cache to grow unacceptably large. The default is 300 seconds (5 minutes). |
| prune_lifetime secs |
| || Specifies, in seconds, the average lifetime of prunes that are sent towards parents. The actual lifetimes will be randomized in the range [.5secs,1.5secs]. The default is 7200 (2 hours). Smaller values cause less state to be kept both at this router and the parent, at the cost of more frequent broadcasts. However, some routers (e.g. mrouted <3.3 and all currently known versions of ciscos IOS) do not use the DVMRP generation ID to determine that a neighbor has rebooted. Prunes sent towards these neighbors should be kept short, in order to shorten the time to recover from a reboot. For use in this situation, the prune_lifetime keyword may be specified on an interface as described below. |
| noflood |
| || The mrouted utility uses a DVMRP optimization to prevent having to keep individual routing tables for each neighbor; part of this optimization is that mrouted assumes that it is the forwarder for each of its attached subnets on startup. This can cause duplicates for a short period (approximately one full route report interval), since both the router that just started up and the proper forwarder will be forwarding traffic. This behavior can be turned off with the noflood keyword; mrouted will not assume that it is the forwarder on startup. Turning on noflood can cause black holes on restart, which will generally last approximately one full route report interval. The noflood keyword can also be specified on individual interfaces. |
| rexmit_prunes [on|off] |
| || Default is to retransmit prunes on all point-to-point interfaces (including tunnels) but no multi-access interfaces. This option may be used to make the default on (or off) for all interfaces. The rexmit_prunes keyword can also be specified on individual interfaces. |
| name "boundary-name scoped-addr/mask-len" |
| || Associates boundary-name with the boundary described by scoped-addr/mask-len, to help make interface configurations more readable and reduce repetition in the configuration file. |
The second section of the configuration file, which may optionally be empty, describes options that apply to physical interfaces.
In addition, the common vif commands described later may all be used on a phyint.
The third section of the configuration file, also optional, describes the configuration of any DVMRP tunnels this router might have.
The common vif commands described below may all be used on tunnels or phyints.
| metric m |
| || The metric is the "cost" associated with receiving a datagram on the given interface or tunnel; it may be used to influence the choice of routes. The metric defaults to 1. Metrics should be kept as small as possible, because DVMRP cannot route along paths with a sum of metrics greater than 31. |
| advert_metric m |
| || The advert_metric is the "cost" associated with sending a datagram on the given interface or tunnel; it may be used to influence the choice of routes. The advert_metric defaults to 0. Note that the effective metric of a link is one ends metric plus the other ends advert_metric. |
| threshold t |
| || The threshold is the minimum IP time-to-live required for a multicast datagram to be forwarded to the given interface or tunnel. It is used to control the scope of multicast datagrams. (The TTL of forwarded packets is only compared to the threshold, it is not decremented by the threshold. Every multicast router decrements the TTL by exactly 1.) The default threshold is 1. |
In general, all multicast routers connected to a particular subnet or tunnel should use the same metric and threshold for that subnet or tunnel.
| rate_limit r |
| || The rate_limit option allows the network administrator to specify a certain bandwidth in Kbits/second which would be allocated to multicast traffic. It defaults 0 (unlimited). |
| boundary "boundary-name|scoped-addr/mask-len" |
| || The boundary option allows an interface to be configured as an administrative boundary for the specified scoped address. Packets belonging to this address will not be forwarded on a scoped interface. The boundary option accepts either a name or a boundary spec. This command may be specified several times on an interface in order to describe multiple boundaries. |
| passive |
| || No packets will be sent on this link or tunnel until we hear from the other end. This is useful for the "server" end of a tunnel that goes over a dial-on-demand link; configure the "server" end as passive and it will not send its periodic probes until it hears one from the other side, so will not keep the link up. If this option is specified on both ends of a tunnel, the tunnel will never come up. |
| noflood |
| || As described above, but only applicable to this interface/tunnel. |
| prune_lifetime secs |
| || As described above, but only applicable to this interface/tunnel. |
| rexmit_prunes "[on|off]" |
| || As described above, but only applicable to this interface/tunnel. Recall that prune retransmission defaults to on for point-to-point links and tunnels, and to off for multi-access links. |
| allow_nonpruners |
| || By default, mrouted refuses to peer with DVMRP neighbors that do not claim to support pruning. This option allows such peerings on this interface. |
| notransit |
| || A specialized case of route filtering; no route learned from an interface marked "notransit" will be advertised on another interface marked "notransit". Marking only a single interface "notransit" has no meaning. |
| accept|deny "(route/mask-len [exact])+" [bidir] |
| || The accept and deny commands allow rudimentary route filtering. The accept command causes mrouted to accept only the listed routes on the configured interface; the deny command causes mrouted to accept all but the listed routes. Only one of accept or deny commands may be used on a given interface. |
The list of routes follows the accept or deny keyword. If the keyword exact follows a route, then only that route is matched; otherwise, that route and any more specific route is matched. For example, deny 0/0 denys all routes, while deny 0/0 exact denys only the default route. The default route may also be specified with the default keyword.
The bidir keyword enables bidirectional route filtering; the filter will be applied to routes on both output and input. Without the bidir keyword, accept and deny filters are only applied on input. Poison reverse routes are never filtered out.
The routing tables look like this:
Virtual Interface Table
Vif Local-AddressMetric Thresh Flags
0 22.214.171.124 subnet: 36.2/16 1 1 querier
pkts in: 3456
pkts out: 2322323
1 126.96.36.199subnet: 36.11/16 1 1 querier
pkts in: 345
pkts out: 3456
2 188.8.131.52 tunnel: 184.108.40.2063 1
peers: 220.127.116.11 (3.255)
pkts in: 34545433
pkts out: 234342
3 18.104.22.168 tunnel: 22.214.171.124 16
Multicast Routing Table (1136 entries)
Origin-Subnet From-Gateway Metric Tmr In-Vif Out-Vifs
36.2 1 45 0 1* 2 3*
36.8 126.96.36.1994 15 2 0* 1* 3*
36.111 20 1 0* 2 3*
In this example, there are four vifs connecting to two subnets and two tunnels. The vif 3 tunnel is not in use (no peer address). The vif 0 and vif 1 subnets have some groups present; tunnels never have any groups. This instance of mrouted is the one responsible for sending periodic group membership queries on the vif 0 and vif 1 subnets, as indicated by the "querier" flags. The list of boundaries indicate the scoped addresses on that interface. A count of the no. of incoming and outgoing packets is also shown at each interface.
Associated with each subnet from which a multicast datagram can originate is the address of the previous hop router (unless the subnet is directly- connected), the metric of the path back to the origin, the amount of time since we last received an update for this subnet, the incoming vif for multicasts from that origin, and a list of outgoing vifs. "*" means that the outgoing vif is connected to a leaf of the broadcast tree rooted at the origin, and a multicast datagram from that origin will be forwarded on that outgoing vif only if there are members of the destination group on that leaf.
The mrouted utility also maintains a copy of the kernel forwarding cache table. Entries are created and deleted by mrouted.
The cache tables look like this:
Multicast Routing Cache Table (147 entries)
Origin Mcast-groupCTmr Age Ptmr IVif Forwvifs
13.2.116/22 188.8.131.523m 2m - 0 1
138.96.48/21 184.108.40.2065m 2m - 0 1
128.9.160/20 220.127.116.113m 2m - 0 1
198.106.194/2418.104.22.1689m 28s 9m 0P
Each entry is characterized by the origin subnet number and mask and the destination multicast group.
The CTmr field indicates the lifetime of the entry. The entry is deleted from the cache table (or refreshed, if traffic is flowing) when the timer decrements to zero. The Age field is the time since this cache entry was originally created. Since cache entries get refreshed if traffic is flowing, routing entries can grow very old.
The Ptmr field is simply a dash if no prune was sent upstream, or the amount of time until the upstream prune will time out.
The Ivif field indicates the incoming vif for multicast packets from that origin. Each router also maintains a record of the number of prunes received from neighboring routers for a particular source and group. If there are no members of a multicast group on any downward link of the multicast tree for a subnet, a prune message is sent to the upstream router. They are indicated by a "P" after the vif number.
The Forwvifs field shows the interfaces along which datagrams belonging to the source-group are forwarded. A "p" indicates that no datagrams are being forwarded along that interface. An unlisted interface is a leaf subnet with no members of the particular group on that subnet. A "b" on an interface indicates that it is a boundary interface, i.e., traffic will not be forwarded on the scoped address on that interface.
An additional line with a ">" as the first character is printed for each source on the subnet. Note that there can be many sources in one subnet. An additional line with a "<" as the first character is printed describing any prunes received from downstream dependent neighbors for this subnet and group.