Ip-precedence flash-override

[massimilianorizzi]

Hi,
I found, in a router configuration, one route-map that "set ip precedence flash-override", but what means?

Thanks

[Mark Elsen]

 Ref : https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_pi/configuration/xe-3s/iri-xe-3s-book/iri-qos-policy-prop-via-bgp.html

 - Look for the string 'precedence'  apparently it relates to QoS

 M.

[massimilianorizzi]

Yeah, I know that it's about a QoS....but I don't understand "flash-override" what it does :)

[Mark Elsen]

 - As you have the command available on your device you can go into configuration mode and enter set ip precedence ? . A list of options will be presented where then flash-override will be listed with a short description of what it does.

 M.

[Georg Pauwen]

Hello,

I think 'flash-override' equals IP precedence value 4. Check table 6.2 in the attached document...

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus1000/sw/4_0/qos/configuration/guide/nexus1000v_qos/qos_6dscp_val.html#21470

[Deepak Kumar]

Duplicate question. Already shared details.

[Joseph W. Doherty]

As others have already noted, it sets the first 3 bits, of the packet's ToS byte, to (binary) 100. BTW, so does setting DSCP to CS4, AF41, AF42 and AF43. The latter, i.e. setting DSCP, also sets the next 3 ToS bits to some value, while IPPrec does not change them.

Setting ToS bits might be seen on a pretty old device that doesn't support DSCP, or a configuration never updated, or perhaps, some clever "trick" in only wanting to reset/set just those first 3 bits.

Also BTW, the "trick" might be more useful for checking the DSCP group. For example, rather than
match ip dscp CS4 AF41 AF42 AF43
you might see
match ip precedence 4