Multi Homing


The multi homing function enables the load to be distributed among multiple routes to a single destination. For example, it allows simultaneous connections to multiple ISPs and sorting of packets based on the connection speed to each ISP. The function also allows packets to be sent via other ISPs when the line is down.

Address conversion using NAT/IP masquerade is required in order to use this function. In a general ISP connection, the ISP allocates a global address space for the user. Therefore, when the user sends out packets to the Internet via the ISP, the source IP address must be an IP address within the allocated global address space. For this reason, to use multiple ISPs, you need to change the source IP address for each ISP. Address conversion is performed on the router in order to achieve this. If you enable this function with the assigned global address without using NAT/IP masquerade, the route information on the remote device side will become problematic and may result in improper operation.

This function is designed for use on a single router and cannot be used among multiple routers. Configuring this function for multiple routers will not only result in packet loss but may also have a negative influence on other communications in the LAN.

Some applications may not work in the multi homing environment. For example, the FTP passive mode may not work correctly. Before implementing multi homing, you should to verify all the applications that will be used.

Connection Overview

              ISP1          ISP2
               |             |
            +-------------------+                global address space
            |        R T        | - - - - - - - - - - - - - - - - - - - -
            +-------------------+                private address space
        |                           |
     +-----+                     +-----+
     | PC1 |                     | PC2 |
     +-----+                     +-----+ 
  • Internal segments are operated using private addresses.
  • The router incorporates the NAT/IP masquerade function and performs address conversion on the traffic to the ISP.
  • Connecting to multiple ISPs using one router
  • The stream hash value is stored for each route, such that the same stream is always routed to the same route.
  • The stored stream hash values will be removed from the memory if the packets of the applicable stream are not relayed for a given length of time (900 seconds).
  • A stream is identified by the source/destination IP address and protocol value (as well as the source/destination port numbers for TCP/UDP).
  • Each route can have a weight; and a new stream is assigned according to the ratio of the route weight.
  • Another route is used when the interface to the ISP is down.
  • Operations spanning over multiple routers are not supported.

Settings Examples

pp1 PPPoE, NAT, Global address
pp2 PPPoE, Masquerade, Terminal type connection

# ip lan1 address
	NAT/The LAN side should be a private address
	 network in order to use masquerade. 

# nat descriptor type 1 nat
# nat descriptor address outer 1
# pp select 1
pp1# pppoe use lan2
pp1# ip pp nat descriptor 1
	Set the NAT to be used for ISP ‘A’. 

pp1# pp auth accept chap pap
pp1# pp auth myname userA passA
pp1# ppp ipcp ipaddress on
pp1# pp enable 1
pp1# pp select none
	Set the information required for connecting to ISP ‘B’. 
	User name: 	userA
	Password: 	passA

# nat descriptor type 2 masquerade
# pp select 2
pp2# ip pp nat descriptor 2
	Set the masquerade to be used for ISP ‘B’. 

pp2# pp auth accept chap pap
pp2# pp auth myname userB passB
pp2# ppp ipcp ipaddress on
pp2# pp enable 2
pp2# pp select none
	Set the information required for connecting to ISP ‘B’. 
	User name: 	userB
	Password: 	passB

# ip route default gateway pp 1 gateway pp 2
# save
	Set the default route for the two ISPs. 


Set the Statistic IP Routing Information

ip route NETWORK gateway GATEWAY1 [PARAMETER] [gateway GATEWAY2 [PARAMETER]...]
no ip route NETWORK [gateway ...]
[Setting Value]
    • default ... Default route
    • IP address ... Destination host/number of mask bits (32 when omitted)
    • IP address
      • where xxx is a decimal number
    • pp PEER_NUM ... Route to the PP interface. When “dlci=dlci” is specified, a route to the frame relay DLCI.
      • PEER_NUM ... Peer number
    • pp anonymous name=NAME
      • NAME ... Name specified by PAP/CHAP authentication
    • dhcp INTERFACE
      • INTERFACE ... Name of the LAN interface or WAN interface operating as DHCP client when using the default gateway provided by DHCP
    • tunnel TUNNEL_NUM ... Route to the tunnel interface
    • Loopback interface name, null interface name
  • PARAMETER ... Multiple parameters below can be specified by delimiting each parameter with a space
    • filter NUMBER [NUMBER..] ... Set a filter-type route
      • NUMBER
        • Filter number (1..21474836) (multiple numbers can be specified by delimiting each number with a space)
    • metric METRIC ... Specify the metric
      • METRIC
        • Metric value (1..15)
        • 1 when omitted.
    • hide ... An option that is valid only when the output interface is LAN, WAN, PP, or TUNNEL and indicates that the route is valid only when the destination is connected
    • weight WEIGHT ... Value indicating the ratio between different routes
      • weight
        • Weight on the route (0..2147483647)
        • 1 when omitted.
    • keepalive ... Valid only when there is reachability to GATEWAY1

Sets the static IP route.
If a filter-type route is specified for the gateway parameter, the filter is applied in the order written, and the matched gateway is selected.
If a matching gateway does not exist or there is no gateway that has filter-type route specified, a gateway that does not have filter-type route specified is selected.
If a gateway that does not have filter-type route specified also does not exist, the processing continues assuming that the route does not exist.
If multiple gateways that do not have filter-type route specified are written, the route is selected using the round robin method at the time the routes are to be used.

If multiple gateways that do not have a filter specified are written, the route that is used when it is to be used is determined by a stream that is identified by the source/destination IP address, protocol, and source/destination port number. The same stream packets are always delivered to the same gateway. If a value is specified for WEIGHT (for example the ratio of the line speeds), the ratio of the stream delivered to the route increases in proportion to the ratio of this value with respect to the WEIGHT values of other gateways.

In all cases, gateways that have the hide keyword specified are valid only when the line is connected. The gateways are not evaluated, if the line is not connected. The loopback and null interfaces are always up, so while you can specify the hide keyword for them, doing so has no meaning.

If you wish to use a certain gateway with higher priority without balancing the load when multiple gateways are set, set the WEIGHT option to 0.


An already existing route can be overwritten.
RTX810 supports bridge interface for INTERFACE parameter in Rev.11.01.23 or later.
RTX5000 does not support WAN interface for INTERFACE parameter.


Set the default gateway to

# ip route default gateway 

The remote network connected through PP1 is

# ip route gateway pp 1 

Load sharing by multihoming: There are two routes as a default gateway: the 128k exclusive line for connecting PP1, and the 64k exclusive line for connecting PP2. Also, when each exclusive line goes down, the route at that time is disabled to prevent loss of packets.

* Simultaneous use of the NAT function and the exclusive line keepalive function is necessary.

# ip route default gateway pp 1 weight 2 hide gateway pp 2 weight 1 hide

If PP1 is active, only PP1 is used. When PP1 is down, PP2 is used.

# ip route gateway pp 1 hide gateway pp 2 weight 0 
[Applicable Models]
RTX5000 RTX810 FWX120

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