Re: [mdnsext] The Scope Swamp: Wireless Considerations

"Yi Yang (yiya)" <yiya@cisco.com> Tue, 06 August 2013 19:50 UTC

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From: "Yi Yang (yiya)" <yiya@cisco.com>
To: Alf Watt <alf.watt@ruckuswireless.com>, "mdnsext@ietf.org" <mdnsext@ietf.org>
Thread-Topic: [mdnsext] The Scope Swamp: Wireless Considerations
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Date: Tue, 6 Aug 2013 19:49:59 +0000
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Subject: Re: [mdnsext] The Scope Swamp: Wireless Considerations
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I agree we must consider difference between wired/wireless networks.

Actually, even for a smaller scope, multicast over 802.11 is still an
expensive operation.

On the other hand, we should de-couple discovery scope from
broadcast/multicast domain.

Yi

 

On 8/5/13 5:47 PM, "Alf Watt" <alf.watt@ruckuswireless.com> wrote:

>Following up from the BoF discussion in Berlin today on scoping of service
>advertisements.
>
>The discussion of scope needs to acknowledge the difference between wired
>and wireless networks.
>
>In all IP networks the size of the broadcast domain is a fundamental
>limitation, as the number of devices on the link increases the broadcast
>traffic begins to consume a larger and larger percentage of the available
>bandwidth. Traditionally large wired networks were segmented along
>physical lines, by floor or wing, for example, with each area being
>assigned a subnet and routed to provide end-to-end connectivity.
>
>Wi-Fi users expect (and the 802.11 protocol requires) that users on a
>single SSID are connected to the same IP network and broadcast domain so
>that they can roam seamlessly anywhere within a particular ESS (which can
>be a building, campus or metro area). Limiting the size of these broadcast
>domains means separating users onto different Wi-Fi networks depending on
>their role, instead of their location.
>
>So for wired networks we have a natural, physical scope depending on the
>physical connection of hosts, in wireless networks we have scopes which
>depend largely on the users access rights (since Wi-Fi is almost always
>the security demarkation in networks).
>
>It¹s also worth nothing that the BCP for broadcast domain size is only 255
>hosts (a /24) which makes the 802.11 ESS requirement for a single
>broadcast domain behind a given ESS difficult to achieve for large
>networks, which is why many Wi-Fi vendors support multicast filtering,
>client isolation and ARP proxies all of which can impact mDNS usability.
>
>Best,
>Alf
>
>FYA http://www.youtube.com/watch?v=-FizhXOW2VM&noredirect=1
>
>
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