{"id":3059,"date":"2022-12-20T16:43:23","date_gmt":"2022-12-20T19:43:23","guid":{"rendered":"http:\/\/lode.uno\/linux-man\/index.php\/2022\/12\/20\/skbmod-action-in-tc-man8\/"},"modified":"2022-12-20T16:43:23","modified_gmt":"2022-12-20T19:43:23","slug":"skbmod-action-in-tc-man8","status":"publish","type":"post","link":"https:\/\/lode.uno\/linux-man\/2022\/12\/20\/skbmod-action-in-tc-man8\/","title":{"rendered":"skbmod action in tc (man8)"},"content":{"rendered":"

skbmod action in tc<\/h1>\n

NAME<\/a>
SYNOPSIS<\/a>
DESCRIPTION<\/a>
OPTIONS<\/a>
EXAMPLES<\/a>
SEE ALSO<\/a> <\/p>\n

\n

NAME <\/a> <\/h2>\n

skbmod – user-friendly packet editor action<\/p>\n

SYNOPSIS <\/a> <\/h2>\n

tc<\/b> … action skbmod<\/b> { set<\/b> SETTABLE<\/i> | swap<\/b> SWAPPABLE<\/i> | ecn<\/b> } [ CONTROL<\/i> ] [ index<\/b> INDEX<\/i> ]<\/p>\n

SETTABLE<\/i> := [ dmac<\/b> DMAC<\/i> ] [ smac<\/b> SMAC<\/i> ] [ etype<\/b> ETYPE<\/i> ]<\/p>\n

SWAPPABLE<\/i> := mac<\/b><\/p>\n

CONTROL<\/i> := { reclassify<\/b> | pipe<\/b> | drop<\/b> | shot<\/b> | continue<\/b> | pass<\/b> }<\/p>\n

DESCRIPTION <\/a> <\/h2>\n

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

OPTIONS <\/a> <\/h2>\n

dmac<\/b> DMAC<\/i><\/p>\n

Change the destination mac to the specified address.<\/p>\n

smac<\/b> SMAC<\/i><\/p>\n

Change the source mac to the specified address.<\/p>\n

etype<\/b> ETYPE<\/i><\/p>\n

Change the ethertype to the specified value.<\/p>\n\n\n\n
<\/td>\n\n

mac<\/b><\/p>\n<\/td>\n

<\/td>\n\n

Used to swap mac addresses.<\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

ecn<\/b><\/p>\n<\/td>\n

<\/td>\n\n

Used to mark ECN Capable Transport (ECT) IP packets as Congestion Encountered (CE). Does not affect Non ECN-Capable Transport (Non-ECT) packets.<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

CONTROL<\/i><\/p>\n

The following keywords allow to control how the tree of qdisc, classes, filters and actions is further traversed after this action.
reclassify<\/b><\/p>\n

Restart with the first filter in the current list.<\/p>\n\n\n\n\n
<\/td>\n\n

pipe<\/b><\/p>\n<\/td>\n

<\/td>\n\n

Continue with the next action attached to the same filter.<\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

drop<\/b><\/p>\n<\/td>\n

<\/td>\n <\/td>\n<\/tr>\n
<\/td>\n\n

shot<\/b><\/p>\n<\/td>\n

<\/td>\n\n

Drop the packet.<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

continue<\/b><\/p>\n

Continue classification with the next filter in line.<\/p>\n\n\n
<\/td>\n\n

pass<\/b><\/p>\n<\/td>\n

<\/td>\n\n

Finish classification process and return to calling qdisc for further packet processing. This is the default.<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

EXAMPLES <\/a> <\/h2>\n

To start, observe the following filter with a pedit action:<\/p>\n

tc filter add dev eth1 parent 1: protocol ip prio 10 <\/p>\n\n\n\n\n\n\n\n\n
<\/td>\n\n

u32 match ip protocol 1 0xff flowid 1:2 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

action pedit munge offset -14 u8 set 0x02 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

munge offset -13 u8 set 0x15 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

munge offset -12 u8 set 0x15 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

munge offset -11 u8 set 0x15 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

munge offset -10 u16 set 0x1515 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

pipe<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

Using the skbmod action, this command can be simplified to:<\/p>\n

tc filter add dev eth1 parent 1: protocol ip prio 10 <\/p>\n\n\n\n\n
<\/td>\n\n

u32 match ip protocol 1 0xff flowid 1:2 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

action skbmod set dmac 02:15:15:15:15:15 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

pipe<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

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:<\/p>\n

tc filter add dev eth5 parent 1: protocol ip prio 10 <\/p>\n\n\n\n\n\n\n
<\/td>\n\n

u32 match ip protocol 1 0xff flowid 1:2 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

action skbmod <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

set etype 0xBEEF <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

set dmac 02:12:13:14:15:16 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

set smac 02:22:23:24:25:26<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

To swap the destination and source mac addresses in the Ethernet header:<\/p>\n

tc filter add dev eth3 parent 1: protocol ip prio 10 <\/p>\n\n\n\n\n
<\/td>\n\n

u32 match ip protocol 1 0xff flowid 1:2 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

action skbmod <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

swap mac<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

Finally, to mark the CE codepoint in the IP header for ECN Capable Transport (ECT) packets:<\/p>\n

tc filter add dev eth0 parent 1: protocol ip prio 10 <\/p>\n\n\n\n\n
<\/td>\n\n

u32 match ip protocol 1 0xff flowid 1:2 <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

action skbmod <\/p>\n<\/td>\n<\/tr>\n

<\/td>\n\n

ecn<\/p>\n<\/td>\n<\/tr>\n<\/table>\n

Only one of set<\/b>, swap<\/b> and ecn<\/b> 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.<\/p>\n

SEE ALSO <\/a> <\/h2>\n

tc<\/b>(8), tc-u32<\/b>(8), tc-pedit<\/b>(8)<\/p>\n

\n","protected":false},"excerpt":{"rendered":"

skbmod – user-friendly packet editor action <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[5,52,4,209],"class_list":["post-3059","post","type-post","status-publish","format-standard","hentry","category-8-administracion-del-sistema","tag-5","tag-administracion","tag-man8","tag-tc-skbmod"],"gutentor_comment":0,"_links":{"self":[{"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/posts\/3059","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/comments?post=3059"}],"version-history":[{"count":0,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/posts\/3059\/revisions"}],"wp:attachment":[{"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/media?parent=3059"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/categories?post=3059"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/tags?post=3059"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}