Subject: RE: Doubt regarding Cache updation in Host

From: Peter Higginson <[email-masked]>
Date: Mon, 29 Dec 1997 21:37:48 -0000

The host ARP table can contain many entries, in the example you give, it
will get

	IP A -> 00 00 5E XX XX 01
	IP B -> 00 00 5E XX XX 02

in all the hosts (or they may get just the ones they need if they fill
their tables from replies to their own requests).

So when hosts H3 and H4 look for the MAC address associated with their
default router (IP B) they get the second MAC address. Similarly H1 and
H2 look for the MAC address associated with IP A and get the first MAC
address.

This does not require a gratuitous ARP (but may make use of it), if the
host needs the MAC address, it will send an ARP request and get the
correct reply.

For your second question, it depends whether you mean the source MAC
address at frame level or the source IP address/MAC address pair in the
ARP data. Assuming the second, each router uses its master IP address
and the corresponding MAC address.

Regards,
Peter

>-----Original Message-----
>From:	raovrn [SMTP:[email-masked]]
>Sent:	30 December 1997 01:51
>To:	'vrrpmls'
>Cc:	basila
>Subject:	Doubt regarding Cache updation in Host
>
>
>Hi,
>
>We have the following doubts regarding the operational aspects of VRRP.
>
>1. Let us consider the following configuration given in VRRP Draft section 
>4.2.
>
>
>>4.2  Sample Configuration 2
>>
>>   The following figure shows a configuration with two virtual routers
>>   with the hosts spitting their traffic between them.
>>
>>                       VRID=1       VRID=2
>>                      +-----+      +-----+
>>                      | MR1 |      | MR2 |
>>                      |  &  |      |  &  |
>>                      | BR2 |      | BR1 |
>>                      +-----+      +-----+
>>         IP A ---------->*            *<---------- IP B
>>                         |            |
>>                         |            |
>>                         |            |
>>       ------------------+------------+-----+--------+--------+--------+--
>>                                            ^        ^        ^        ^
>>                                            |        |        |        |
>>                                          (IP A)   (IP A)   (IP B)   (IP B)
>>                                            |        |        |        |
>>                                         +--+--+  +--+--+  +--+--+  +--+--+
>>                                         |  H1 |  |  H2 |  |  H3 |  |  H4 |
>>                                         +-----+  +-----+  +--+--+  +--+--+
>>
>>      Legend:
>>               ---+---+---+--  =  802 network, Ethernet or FDDI
>>                            H  =  Host computer
>>                           MR  =  Master Router
>>                           BR  =  Backup Router
>>                            *  =  IP Address
>>                         (IP)  =  default router for hosts
>
>
>In the virtual router VRID 1, the Master IP Address is IP "A", and 
>associated IP Address is IP "B". Similarly, for VRID 2, the Master IP 
>Address is IP "B", and associated IP Address is IP "A".
>
>When router VRID 1 sends the gratuitous ARP request, the ARP cache in all 
>the hosts will be updated with the virtual MAC address "00 00 5E XX XX 01". 
>Host H3 and H4 ARP cache should be updated with virtual MAC address "00 00 
>5E XX XX 02" which will not happen because gratuitous ARP request is sent to 
>all the associated IP addresses also. A similar situation arises, if VRID 2 
>sends gratuitous request.
>
>Pl. correct us if we are wrong on this assumption.
>
>
>If this assumption is correct, how do we make the hosts H3 and H4 have 
>virtual MAC address "00 00 5E XX XX 02".
>
>How does load sharing occur, if all the hosts have the same virtual MAC 
>address.
>
>
>
>2. Also, we are curious to know how the virtual MAC address gets filled up 
>during ARP request/reply as source MAC address ?
>
>We would appreciate if someone in the mailing list could help us in 
>clarifying these questions.
>
>Regards,
>Rao & Basil
>
>
>V.R.N. Rao & Anton Basil
>Future Software Pvt., Ltd.,
>481, Nandanam,
>Madras - 600 035.
>
>Voice : 91-44-4340323, 4330550 (Extn : 331)
>Fax : 91-44-4344157, 4834551, 4834661
>Email : [email-masked], [email-masked]
>