Allied Telesis AT-WR4500 manual Nat

AT-WR4500 Series - IEEE 802.11abgh Outdoor Wireless Routers	111
RouterOS v3 Configuration and User Guide

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Description

RouterOS has following types of routes:

dynamic routes - automatically created routes for networks, which are directly accessed through an interface. They appear automatically, when adding a new IP address. Dynamic routes are also added by routing protocols.

static routes - user-defined routes that specify the router which can forward traffic to the specified destination network. They are useful for specifying the default gateway. The gateway for static routes may be checked (with either ARP or ICMP protocol) for reachability, so that different gateways with different priorities (costs) may be assigned for one destination network to provide failover.

ECMP (Equal Cost Multi-Path) Routing

This routing mechanism enables packet routing along multiple paths with equal cost and ensures load balancing. With ECMP routing, you can use more than one gateway for one destination network (this approach may also be configured to provide failover). With ECMP, a router potentially has several available next hops towards a given destination. A new gateway is chosen for each new source/destination IP pair. It means that, for example, one FTP connection will use only one link, but new connection to a different server will use another link. ECMP routing has another good feature - single connection packets do not get reordered and therefore do not kill TCP performance.

The ECMP routes can be created by routing protocols (RIP or OSPF), or by adding a tatic route with multiple gateways, separated by a comma (e.g., /ip route add gateway=192.168.0.1,192.168.1.1). The routing protocols may create multipath dynamic routes with equal cost automatically, if the cost of the interfaces is adjusted propery. For more information on using routing protocols, please read the corresponding Manual.

Policy-Based Routing

It is a routing approach where the next hop (gateway) for a packet is chosen, based on a policy, which is configured by the network administrator. In RouterOS the procedure the follwing:

•mark the desired packets, with a routing-mark

•choose a gateway for the marked packets

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In routing process, the router decides which route it will use to send out the packet. Afterwards, when the packet is masqueraded, its source address is taken from the prefsrc field.

5.4.2 Routes

Submenu level: /ip route

Description

In this submenu you can configure Static, Equal Cost Multi-Path and Policy-Based Routing and see the routes.

Property Description

bgp-as-path(text) - manual value of BGP's as-path for outgoing route bgp-atomic-aggregate(yes no) - indication to receiver that it cannot "deaggregate" the prefix bgp-communities(multiple choice: integer) - administrative policy marker, that can travel through different autonomous systems

internet - communities value 0

bgp-local-pref(integer) - local preference value for a route

bgp-med(integer) - a BGP attribute, which provides a mechanism for BGP speakers to convey to an adjacent AS the optimal entry point into the local AS