Subject: [Isis-wg] Circuit ID field in IS-IS Hello PDUs

From: Ashish Zalani <[email-masked]>
Date: Fri, 02 Nov 2001 12:54:55 -0500

Hi,

I am relatively new to IS-IS and am trying to understand how IS-IS PDUs are 
handled. Specifically, I am curious to know how the Circuit ID field in a 
Point-to-Point IIH (or the LAN ID field in a L1/L2 LAN IIH) is assigned.

 From what I understand, the circuit ID is a 1-byte field that uniquely 
identifies the interface on the system. That would allow for a maximum of 
255 interfaces. What happens if the number of (connected) interfaces on a 
router is more than 255? How is the circuit ID ensured to be unique among 
all interfaces?

Thanks,
-Ashish.
Ashish Zalani	
Modeling Engineer
OPNET Technologies, Inc.

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Isis-wg mailing list  -  [email-masked]
http://external.juniper.net/mailman/listinfo/isis-wg

---

From: Naiming Shen <[email-masked]>
Date: Sun, 04 Nov 2001 02:00:19 -0800

For p2p isis interface, the best algorithm:

circuit_id =
  ( slot_id * 1 + port_id * 2 + channel_id * 3 + dlci_num + vci * vpi +
    vlan_cid * 4 + interface_dwdm_wave_length_in_nm * 5 +
    uniform_distributed_ramdom_number(0, 2**24 - 1) +
    max(1200, seconds_laps_since_January_3_1997) +
    cost_of_router_in_euros ) % 255;

For LAN isis interface, just make sure it's unique and not exceeding 255.
if more than 255 LAN intf on a router is needed, tricky mechanism is required.

thanks.

 ]Hi,
 ]
 ]I am relatively new to IS-IS and am trying to understand how IS-IS PDUs are 
 ]handled. Specifically, I am curious to know how the Circuit ID field in a 
 ]Point-to-Point IIH (or the LAN ID field in a L1/L2 LAN IIH) is assigned.
 ]
 ] From what I understand, the circuit ID is a 1-byte field that uniquely 
 ]identifies the interface on the system. That would allow for a maximum of 
 ]255 interfaces. What happens if the number of (connected) interfaces on a 
 ]router is more than 255? How is the circuit ID ensured to be unique among 
 ]all interfaces?
 ]
 ]Thanks,
 ]-Ashish.
 ]Ashish Zalani	
 ]Modeling Engineer
 ]OPNET Technologies, Inc.
 ]
 ]_______________________________________________
 ]Isis-wg mailing list  -  [email-masked]
 ]http://external.juniper.net/mailman/listinfo/isis-wg

- Naiming