路由问题

郁金香

环境linux

eth0 192.168.0.1
eth1 202.106.x.x
eth2 219.142.x.x

默认网关202.106.x.1
用户192.168.0.0/24 通过192.168.0.1 访问internet 默认是走202.106.x.x这条线路
如果现在想让用户192.168.0.5 访问internet走219.142.x.x 这条线路如何实现呢?(网关219.142.x.1)
要iptables和iproute2 一起来实现吗?

[ 本帖最后由 郁金香 于 2007-2-13 16:49 编辑 ]

ssffzz1

LZ说的对，现用iptables对5的包打标识，然后建立一个针对标识的路由表就客一了。

HonestQiao

可参考：http://fanqiang.chinaunix.net/system/linux/2006-05-30/4355.shtml

或者：http://blog.chinaunix.net/u/4543/showart_24558.html
电信,网通双线实战

mrfan

这个跟双线无关吧，只是简单的源地址策略路由而已

ip ro replace default via 219.142.x.x  dev eth2 table 2
ip ru add from 192.168.0.5 table 2

billjie1

Routing for multiple uplinks/providers
A common configuration is the following, in which there are two providers that connect a local network (or even a single machine) to the big Internet.

                                                                 ________
                                          +------------+        /
                                          |            |       |
                            +-------------+ Provider 1 +-------
        __                  |             |            |     /
    ___/  \_         +------+-------+     +------------+    |
  _/        \__      |     if1      |                      /
/             \     |              |                      |
| Local network -----+ Linux router |                      |     Internet
\_           __/    |              |                      |
   \__     __/       |     if2      |                      \
      \___/          +------+-------+     +------------+    |
                            |             |            |     \
                            +-------------+ Provider 2 +-------
                                          |            |       |
                                          +------------+        \________

There are usually two questions given this setup.

4.2.1. Split access
The first is how to route answers to packets coming in over a particular provider, say Provider 1, back out again over that same provider.

Let us first set some symbolical names. Let $IF1 be the name of the first interface (if1 in the picture above) and $IF2 the name of the second interface. Then let $IP1 be the IP address associated with $IF1 and $IP2 the IP address associated with $IF2. Next, let $P1 be the IP address of the gateway at Provider 1, and $P2 the IP address of the gateway at provider 2. Finally, let $P1_NET be the IP network $P1 is in, and $P2_NET the IP network $P2 is in.

One creates two additional routing tables, say T1 and T2. These are added in /etc/iproute2/rt_tables. Then you set up routing in these tables as follows:


          ip route add $P1_NET dev $IF1 src $IP1 table T1
          ip route add default via $P1 table T1
          ip route add $P2_NET dev $IF2 src $IP2 table T2
          ip route add default via $P2 table T2
       
Nothing spectacular, just build a route to the gateway and build a default route via that gateway, as you would do in the case of a single upstream provider, but put the routes in a separate table per provider. Note that the network route suffices, as it tells you how to find any host in that network, which includes the gateway, as specified above.

Next you set up the main routing table. It is a good idea to route things to the direct neighbour through the interface connected to that neighbour. Note the `src' arguments, they make sure the right outgoing IP address is chosen.

            ip route add $P1_NET dev $IF1 src $IP1
            ip route add $P2_NET dev $IF2 src $IP2
          
Then, your preference for default route:
            ip route add default via $P1
          
Next, you set up the routing rules. These actually choose what routing table to route with. You want to make sure that you route out a given interface if you already have the corresponding source address:
            ip rule add from $IP1 table T1
            ip rule add from $IP2 table T2
          
This set of commands makes sure all answers to traffic coming in on a particular interface get answered from that interface.



Reader Rod Roark notes: 'If $P0_NET is the local network and $IF0 is its interface, the following additional entries are desirable:

ip route add $P0_NET     dev $IF0 table T1
ip route add $P2_NET     dev $IF2 table T1
ip route add 127.0.0.0/8 dev lo   table T1
ip route add $P0_NET     dev $IF0 table T2
ip route add $P1_NET     dev $IF1 table T2
ip route add 127.0.0.0/8 dev lo   table T2                                      
'



Now, this is just the very basic setup. It will work for all processes running on the router itself, and for the local network, if it is masqueraded. If it is not, then you either have IP space from both providers or you are going to want to masquerade to one of the two providers. In both cases you will want to add rules selecting which provider to route out from based on the IP address of the machine in the local network.

4.2.2. Load balancing
The second question is how to balance traffic going out over the two providers. This is actually not hard if you already have set up split access as above.

Instead of choosing one of the two providers as your default route, you now set up the default route to be a multipath route. In the default kernel this will balance routes over the two providers. It is done as follows (once more building on the example in the section on split-access):

            ip route add default scope global nexthop via $P1 dev $IF1 weight 1 \
            nexthop via $P2 dev $IF2 weight 1
          
This will balance the routes over both providers. The weight parameters can be tweaked to favor one provider over the other.

Note that balancing will not be perfect, as it is route based, and routes are cached. This means that routes to often-used sites will always be over the same provider.

Furthermore, if you really want to do this, you probably also want to look at Julian Anastasov's patches at http://www.ssi.bg/~ja/#routes , Julian's route patch page. They will make things nicer to work with.

platinum

http://bbs.chinaunix.net/viewthread.php?tid=304033