Mac address and VLAns
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Posted by vicky on June 17, 2008, 1:27 am
Please log in for more thread options Plz explain ... A single mac address is able to be a member of multiple vlans. VIkrant | |||||||||||||||||||||||||||||||||||||
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Posted by Walter Roberson on June 17, 2008, 8:09 am
Please log in for more thread options > Plz explain ...
> A single mac address is able to be a member of multiple vlans.
MAC addresses need not be globally unique: they only have to be unique within the broadcast domain. Broadcast domains can be physically seperated (different segments), or can use different protocols, or can be logically seperated (different VLANs.) | |||||||||||||||||||||||||||||||||||||
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Posted by Rich Seifert on June 17, 2008, 11:05 am
Please log in for more thread options In article
> Hi,
> > Plz explain ... > > A single mac address is able to be a member of multiple vlans. > A MAC address is not a "member" of a VLAN. It is *frames* (not MAC addresses, ports, IP addresses, or anything else) that are associated with particular VLANs. The rules for associating frames with VLANs can be based on almost any characteristic of the frame, such as: -the switch port on which the frame arrived (port-based VLAN) -the MAC source address in the frame (MAC address-based VLAN) -the IP subnet identifier within the frame (IP subnet-based VLAN) -the TCP/UDP port number within the frame (application-based VLAN), etc. While many people may *think* they are associating a port (or a MAC address) with a VLAN, they are really specifying a VLAN-association rule that is based on switch port (or MAC address); the distinction is subtle, but important, particularly when end stations are VLAN-aware, and perform the association themselves. Consider a multi-homed VLAN-aware end station (e.g., a server) that associates frames with VLANs based on IP subnet identifiers. Since that station has multiple IP addresses (that's what multi-homed means), it will emit frames carrying different VLAN IDs, depending on the subnet to which the frame is directed. However, that station may have the same MAC address on all subnets (sidebar: I never said that the server had multiple physical interfaces, and even if it did, it is permissible to assign the same MAC address to multiple interfaces that are not on the same LAN). Thus, this is a device that, according to *your* model, has a MAC address that is a "member" of multiple VLANs. This dichotomy disappears when one realizes that it is the *frames* that are associated with the VLANs, and each frame is associated with one (and only one) VLAN. If you don't like the multi-homed station example, the same phenomenon arises in the case of a single-homed station that associates VLAN IDs based on application streams; e.g., a video delivery server (think: Intranet multicast delivery of training videos) that assigns a VLAN to each video stream so that bandwidth can be conserved within an enterprise. Another example is a VoIP conference-call server, associating each conference call (multicast) to a VLAN. There is a complete explanation of this in Chapter 11 of "The Switch Book." -- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX Send replies to: usenet at richseifert dot com | |||||||||||||||||||||||||||||||||||||
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Posted by vicky on June 20, 2008, 12:04 am
Please log in for more thread options wrote:
> In article
> > > Hi,
>
> > =A0 =A0 =A0 =A0Plz explain =A0...
>
> > =A0 =A0 =A0 =A0 A single mac address is able to be a member of multiple=
vlans.
>
lting
> A MAC address is not a "member" of a VLAN. It is *frames* (not MAC > addresses, ports, IP addresses, or anything else) that are associated > with particular VLANs. The rules for associating frames with VLANs can > be based on almost any characteristic of the frame, such as: > > -the switch port on which the frame arrived (port-based VLAN) > -the MAC source address in the frame (MAC address-based VLAN) > -the IP subnet identifier within the frame (IP subnet-based VLAN) > -the TCP/UDP port number within the frame (application-based VLAN), etc. > > While many people may *think* they are associating a port (or a MAC > address) with a VLAN, they are really specifying a VLAN-association rule > that is based on switch port (or MAC address); the distinction is > subtle, but important, particularly when end stations are VLAN-aware, > and perform the association themselves. > > Consider a multi-homed VLAN-aware end station (e.g., a server) that > associates frames with VLANs based on IP subnet identifiers. Since that > station has multiple IP addresses (that's what multi-homed means), it > will emit frames carrying different VLAN IDs, depending on the subnet to > which the frame is directed. However, that station may have the same MAC > address on all subnets (sidebar: I never said that the server had > multiple physical interfaces, and even if it did, it is permissible to > assign the same MAC address to multiple interfaces that are not on the > same LAN). Thus, this is a device that, according to *your* model, has a > MAC address that is a "member" of multiple VLANs. This dichotomy > disappears when one realizes that it is the *frames* that are associated > with the VLANs, and each frame is associated with one (and only one) > VLAN. > > If you don't like the multi-homed station example, the same phenomenon > arises in the case of a single-homed station that associates VLAN IDs > based on application streams; e.g., a video delivery server (think: > Intranet multicast delivery of training videos) that assigns a VLAN to > each video stream so that bandwidth can be conserved within an > enterprise. Another example is a VoIP conference-call server, > associating each conference call (multicast) to a VLAN. > > There is a complete explanation of this in Chapter 11 of "The Switch > Book." > > -- > Rich Seifert =A0 =A0 =A0 =A0 =A0 =A0 =A0Networks and Communications Consu= > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 21885 Bear Creek Way
> (408) 395-5700 =A0 =A0 =A0 =A0 =A0 =A0Los Gatos, CA 95033 > (408) 228-0803 FAX > > Send replies to: usenet at richseifert dot com ------------------------------------------------------------------ Sir ... As u mentioned about a book .... The Switch Book... can u plz ... give a full detail of this book (publication, writer etc) so that it is easy for me to find it at book stores.... Vikrant. | |||||||||||||||||||||||||||||||||||||
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Posted by jpd on June 20, 2008, 1:30 am
Please log in for more thread options On Thu, 19 Jun 2008 21:04:01 -0700 (PDT),
> Sir ...
> > As u mentioned about a book .... The Switch Book... > can u plz ... give a full detail of this book (publication, writer > etc) > so that it is easy for me to find it at book stores.... > > Vikrant. For example, see here: http://www.amazon.com/Switch-Book-Complete-Switching-Technology/dp/0471345865 Finding this cost me less than 10 seconds, even without using the knowledge who the author is (which anyone regularly reading this group knows). I don't know about you, but that is less than the time it took me to write this followup posting. -- j p d (at) d s b (dot) t u d e l f t (dot) n l . This message was originally posted on Usenet in plain text. Any other representation, additions, or changes do not have my consent and may be a violation of international copyright law. | |||||||||||||||||||||||||||||||||||||
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