tcpbridge¶

Bridges two network segments, optionally rewriting packets as they cross. Where tcpreplay sends a saved capture, tcpbridge forwards live traffic between two interfaces — applying the same libtcpedit rewriting engine as tcprewrite to each packet in flight.

tcpbridge [OPTION]... --intf1=<ethA> --intf2=<ethB>

Forwards live traffic — needs root

tcpbridge moves real packets between real interfaces. Use it only on lab segments you control.

What it's for¶

tcpbridge is useful when you want a device or host to see modified live traffic without changing the source. Sitting between two segments, it can, for example:

rewrite addresses or VLAN tags so traffic from one lab network appears to come from another;
normalize or mangle headers to test how a downstream device copes;
convert between link-layer types across the bridge.

Basic use¶

$ sudo tcpbridge --intf1=eth0 --intf2=eth1

By default it forwards frames between eth0 and eth1. Add any tcprewrite editing option to transform packets as they pass:

$ sudo tcpbridge --intf1=eth0 --intf2=eth1 \
    --pnat=10.0.0.0/8:192.168.0.0/16 \
    --enet-vlan=del \
    --fixcsum

Direction and filtering¶

Because a bridge inherently has two sides, the rewriting options that take separate client/server values apply naturally: traffic entering --intf1 is one direction, --intf2 the other. You can also limit which traffic is bridged with the same include/exclude and filtering options the other tools use.

When to reach for something else¶

To send a saved capture rather than forward live traffic, use tcpreplay.
To edit a capture into a file without any network, use tcprewrite.