Subject: Doubt regarding Cache updation in Host

From: raovrn <[email-masked]>
Date: Mon, 29 Dec 97 17:51:00 PST

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]

---

From: Acee Lindem <[email-masked]>
Date: Mon, 29 Dec 1997 15:29:22 -0500 (EST)

> How does load sharing occur, if all the hosts have the same virtual MAC 

H1 and H2 have IP A as their default gateway address while H3 and H4 have
IP B as their default address. So, when both VR's are available you have
the 4 hosts distributed equally over the 2 routers. 

> during ARP request/reply as source MAC address ?

You need a layer-2 API to provide the source MAC address when sending
packets. Luckily, we already had a fast-path interface to provide a
previously cached MAC header. Hence this wasn't much of a problem for us. 

Acee