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Re: [v6ops] MAC table shortage in IPv6 networks caused by multiple IPv6 prefixes/addresses//FW: New Version Notification for draft-liu-v6ops-running-multiple-prefixes-01.txt

"Eric Vyncke (evyncke)" <evyncke@cisco.com> Fri, 11 July 2014 10:28 UTC

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From: "Eric Vyncke (evyncke)" <evyncke@cisco.com>
To: "Liubing (Leo)" <leo.liubing@huawei.com>, "Andrew Yourtchenko (ayourtch)" <ayourtch@cisco.com>
Thread-Topic: [v6ops] MAC table shortage in IPv6 networks caused by multiple IPv6 prefixes/addresses//FW: New Version Notification for draft-liu-v6ops-running-multiple-prefixes-01.txt
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Date: Fri, 11 Jul 2014 10:28:22 +0000
Message-ID: <CFE58894.20BA4%evyncke@cisco.com>
References: <8AE0F17B87264D4CAC7DE0AA6C406F453D8EEA21@nkgeml506-mbx.china.huawei.com> <8AE0F17B87264D4CAC7DE0AA6C406F453D8F1C32@nkgeml506-mbx.china.huawei.com> <alpine.DEB.2.02.1407091226000.7929@uplift.swm.pp.se> <CFE32281.2067C%evyncke@cisco.com> <alpine.DEB.2.02.1407091710020.7929@uplift.swm.pp.se> <alpine.OSX.2.00.1407091840270.99248@ayourtch-mac> <8AE0F17B87264D4CAC7DE0AA6C406F453D8F291C@nkgeml506-mbx.china.huawei.com> <alpine.OSX.2.00.1407101220310.93503@ayourtch-mac> <8AE0F17B87264D4CAC7DE0AA6C406F453D8F2AB4@nkgeml506-mbx.china.huawei.com> <alpine.OSX.2.00.1407111029250.37292@ayourtch-mac> <8AE0F17B87264D4CAC7DE0AA6C406F453D8F2AF9@nkgeml506-mbx.china.huawei.com>
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Subject: Re: [v6ops] MAC table shortage in IPv6 networks caused by multiple IPv6 prefixes/addresses//FW: New Version Notification for draft-liu-v6ops-running-multiple-prefixes-01.txt
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Regarding cache space (and no cache entry count), please note that the IP
address is only part of the entry, there are many other bytes (counters
for example) which also reside in this entry. So, it is not comparing 4
bytes vs. 16 bytes but rather comparing n+4 bytes vs. n+16 bytes (where n
> 16 in most implementations I would guess)

-éric

On 11/07/14 11:40, "Liubing (Leo)" <leo.liubing@huawei.com> wrote:

>Hi Andrew,
>
>> > Now there are some enterprise/campus networks under real use or
>> >considering using L2 networks. Some are aiming at better user isolation
>> >through VLANs (some even consider QinQ mechanism); while some are
>> >aiming less configuration/management than the traditional L3 networks.
>> >So there would be thousands of hosts aggregated to the core switch
>> >(normally there are two core switches stacked together, but only share
>>one
>> cache space).
>> >As IPv6 is beginning real use, for example, some of the campus networks
>> >are already dual-stack, and the majority of the hosts are Win 7, we
>> >once observed in one campus that DHCPv6/SLAAC are both enabled, each
>> >Win 7 host had 4 IPv6 addr (SLAAC+DHCPv6+Privacy+link-local)+1 IPv4
>>addr.
>> 
>> If the majority of the hosts are Win 7, and are under the control of the
>> administrator, this looks more like a misconfiguration rather than
>>anything
>> else: clear the "A" bit on the prefix, and they'll half the address
>>usage - down
>> to just link-local and DHCPv6-based.
>
>[Bing] I can hardly say SLAAC and DHCPv6 co-existing is a
>misconfiguration, but I agree DHCPv6-only deployment can partly relieve
>the problem.
>However, even DHCPv6-only would have 2 IPv6 addr+1 IPv4 addr, which would
>cause approximately 5~8 times cache space than IPv4-only.
>
>Best regards,
>Bing
>
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