---
name: "tc-skbmod"
section: "8"
platform: "linux"
package: "iproute2"
version: "7.3.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/tc-skbmod"
---

# tc-skbmod(8)

user-friendly packet editor action

## NAME

skbmod - user-friendly packet editor action

## SYNOPSIS

**tc** ... **action skbmod** { **set**  *SETTABLE* \|  **swap** *SWAPPABLE*  \| **ecn** } \[ *CONTROL* \] \[  **index** *INDEX*  \]

*SETTABLE* :=   \[ **dmac** *DMAC* \]   \[ **smac** *SMAC* \]   \[ **etype** *ETYPE* \]

*SWAPPABLE* :=  **mac**

*CONTROL* := { **reclassify** \| **pipe** \| **drop** \| **shot** \| **continue** \| **pass** }

## DESCRIPTION

The **skbmod** action is intended as a usability upgrade to the existing **pedit** action. Instead of having to manually edit 8-, 16-, or 32-bit chunks of an ethernet header, **skbmod** allows complete substitution of supported elements. Action must be one of **set**, **swap** and **ecn**. **set** and **swap** only affect Ethernet packets, while **ecn** only affects IP packets.

## OPTIONS

- **dmac** *DMAC*

  Change the destination mac to the specified address.

- **smac** *SMAC*

  Change the source mac to the specified address.

- **etype** *ETYPE*

  Change the ethertype to the specified value.

- **mac**

  Used to swap mac addresses.

- **ecn**

  Used to mark ECN Capable Transport (ECT) IP packets as Congestion Encountered (CE). Does not affect Non ECN-Capable Transport (Non-ECT) packets.

- *CONTROL*

  The following keywords allow one to control how the tree of qdisc, classes, filters and actions is further traversed after this action.

  - **reclassify**

    Restart with the first filter in the current list.

  - **pipe**

    Continue with the next action attached to the same filter.

  - **drop** **shot**

    Drop the packet.

  - **continue**

    Continue classification with the next filter in line.

  - **pass**

    Finish classification process and return to calling qdisc for further packet processing. This is the default.

## EXAMPLES

To start, observe the following filter with a pedit action:

```
tc filter add dev eth1 parent 1: protocol ip prio 10 \
	u32 match ip protocol 1 0xff flowid 1:2 \
	action pedit munge offset -14 u8 set 0x02 \
	munge offset -13 u8 set 0x15 \
	munge offset -12 u8 set 0x15 \
	munge offset -11 u8 set 0x15 \
	munge offset -10 u16 set 0x1515 \
	pipe
```

Using the skbmod action, this command can be simplified to:

```
tc filter add dev eth1 parent 1: protocol ip prio 10 \
	u32 match ip protocol 1 0xff flowid 1:2 \
	action skbmod set dmac 02:15:15:15:15:15 \
	pipe
```

Complexity will increase if source mac and ethertype are also being edited as part of the action. If all three fields are to be changed with skbmod:

```
tc filter add dev eth5 parent 1: protocol ip prio 10 \
	u32 match ip protocol 1 0xff flowid 1:2 \
	action skbmod \
	set etype 0xBEEF \
	set dmac 02:12:13:14:15:16 \
	set smac 02:22:23:24:25:26
```

To swap the destination and source mac addresses in the Ethernet header:

```
tc filter add dev eth3 parent 1: protocol ip prio 10 \
	u32 match ip protocol 1 0xff flowid 1:2 \
	action skbmod \
	swap mac
```

Finally, to mark the CE codepoint in the IP header for ECN Capable Transport (ECT) packets:

```
tc filter add dev eth0 parent 1: protocol ip prio 10 \
	u32 match ip protocol 1 0xff flowid 1:2 \
	action skbmod \
	ecn
```

Only one of **set**, **swap** and **ecn** shall be used in a single command. Trying to use more than one of them in a single command is considered undefined behavior; pipe multiple commands together instead.

## SEE ALSO

[**tc**(8)](/tc/8.md), [**tc-u32**(8)](/tc-u32/8.md), [**tc-pedit**(8)](/tc-pedit/8.md)