What role do routing options play in a LANCOM router?


IP router enabled:
You can use the IP router module to connect IP networks with one another or to connect your local network to the Internet.
If the router is simply used as a bridge (same address range on each side – see selection field Bridge) the module must be
disabled. The bridge function is not supported by all LANCOM routers.

Use Proxy ARP to tie remote stations into the LAN:
Use this option to integrate remote computers into your local network as if they were connected locally (RAS dial-in).

Send ICMP redirects:
Each packet received for which a local route exists is answered with an ICMP redirect if the packet source is situated in the local network. The packet itself is forwarded to the appropriate router. This option is enabled in the default settings.
When the option is disabled, no ICMP redirects will be sent, and the packets will only be sent to the appropriate router.

Transfer ICMP packets secured:
This setting causes the LANCOM router wherever possible not to reject ICMP packets.

There are three possibilities when transmitting packets:

1. The packet is given priority
2. The packet is transmitted normally
3. The packet is transmitted secured

A packet given priority will always be transmitted before all other waiting packets.

Packets to be transmitted normally or secured will be sent in the sequence in which they were received. The secured status becomes important at the moment when the LANCOM router has to discard packets. Before a "secured" packet is discarded, the router will first discard all normal and then all prioritized packets waiting for transmission. A secured packet will only be discarded when no other packet can be discarded.

This is used in combination with the setting "Routing method: TOS", where the Type Of Service field of an IP packet is evaluated:
  • All packets with the Low Delay Flag set will be given priority for transmission.
  • All packets with High Reliability Flag set will be transmitted secured
  • All other packets will be transmitted as normal.

With the "Transfer ICMP packets secured" setting, the LANCOM router treats received ICMP packets as if the High Reliability Flag in the TOS field were set.

Pass on TCP-SYN and ACK packets preferentially:
TCP packets with no payload data are given preference for transmission. Let us suppose that you are performing a download and an upload
simultaneously. If there is a large amount of traffic, the download will be slowed down since SYN packets from the computer would spend longer in the router's queue before being transmitted.
Activating this option puts these packets into the 'fast lane'.

Transfer packets from internal services via the router:
By default, local services always bypass the router. Acknowledgements are always sent back directly to the MAC address where the request originated. Select this option if you wish packets from internal services to be sent via the router. Packets will then be sent not directly to the MAC address of the sender but via the router, provided an appropriate route has been configured.

Note the Type-Of-Service field in IP packets:
This option specifies how the router should behave when transmitting IP packets. The router evaluates certain options in the IP packets
that indicate whether the packets should be transmitted particularly fast or secured.

Interpret the DiffServ field in IP packets:
The router will interpret the DiffServ field in IP packets and then use standardized DSCP (DiffServ code point) AFxx (Assured Forwarding) for secured transmission and EF (Expedited Forwarding) for preferential transmission. All other IP packets will be transmitted normally.

Note: This option cannot be used in combination with ToS since the DiffServ field replaces the ToS field within the IP packet.

Copy DiffServ tags from Layer-3 to Layer-2:
This switch causes Diffserv tags in layer 3 to be copied to layer 2.
Existing tags at layer 2 will be overwritten.

DiffServ tags from Layer-2:
There are three options:
    - Ignore:
    Diffserv tags at layer 2 will be overwritten.

    - Copy to Layer-3:
    The DiffServ field from layer 2 will be copied to layer 3. This option always overwrites the field at layer 3 even if there is no tag set in layer 2.

    - Copy automatically:
    The DiffServ tag from layer 2 will only be copied to layer 3 if it is set and there is no tag set in layer 3.