mikey250
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ISL & 802.1q
ISL - has some of the following which im aware of:
- Has 30 byte encapsulation
- 26 byte header
- 4 byte cyclic redundancy check or FSC
- 3 COS bit filed used for (class of service) - is this related to VOIP?
Also
802.1q
Does 802.1p - which states the following:
Made up of 4 headers
- Ethertype: 0x8100
- 802.1P: 3 COS bits used for QOS Marking - is this referring to VOIP? & as ISL is more superior than 802.1q how come QOS Markings is NOT included in ISL?
- Token ring flag: 1 bit
- Vlan id: 12 bits (1-4094 range for vlans)
- Has 30 byte encapsulation
- 26 byte header
- 4 byte cyclic redundancy check or FSC
- 3 COS bit filed used for (class of service) - is this related to VOIP?
Also
802.1q
Does 802.1p - which states the following:
Made up of 4 headers
- Ethertype: 0x8100
- 802.1P: 3 COS bits used for QOS Marking - is this referring to VOIP? & as ISL is more superior than 802.1q how come QOS Markings is NOT included in ISL?
- Token ring flag: 1 bit
- Vlan id: 12 bits (1-4094 range for vlans)
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how can 802.1q being 'untagged' be handy in some situations, as im lead to believe due to vlan hopping and changing the native vlan 1 to say 99 or anything else is a way round to ensure protection?
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ASKER
hi kdearingm, are you saying 802.1q is better or other way round as 4 bytes is for 802.1q and 30 bytes is for ISL?
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ISL can only use 'MST' for example then if vlans need to cross trunks!
ASKER
hi diepes, "How is native (untagged) vlan handy ? e.g. Want to use a linux server to sniff traffic on different vlans, but need to set it up from a remote location." - Just to clarify my reading, are you saying if 802.1q is used and obviously untagged, specifically on a linux server to sniff traffice then this makes it handy?
1. Change switch port to trunk with native vlan same as linux server's current subnet. - Yes im aware switching the remote connection to 'trunk' allows this!!!
"With ISL you would loose connectivity to the server/router, but not with 802.1q server will work fine on untagged vlan." - I did not realise ISL would loose connectivity but it does makes sense because traffice is secure and protected and not left open due to header info.
1. Change switch port to trunk with native vlan same as linux server's current subnet. - Yes im aware switching the remote connection to 'trunk' allows this!!!
"With ISL you would loose connectivity to the server/router, but not with 802.1q server will work fine on untagged vlan." - I did not realise ISL would loose connectivity but it does makes sense because traffice is secure and protected and not left open due to header info.
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hi diepes, "This is less risky as first change is on switch and if server is not visible can be reversed before vlan's added on server/router device." - I did not get this statement?
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i suppose because im comparing 4 bytes is less than 30 bytes that 30 bytes was better but i accept but did not know 802.1q was better. It was taught that ISL is protected but dont remember them saying it was better although more than likely they probably said 802.1q was preferred i suppose!! thanks for advice!!
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