ISIS auto-cost (reference-bandwidth)

[lv_cuongvt]

Hi All.

From below document on www.cisco.com i wonder if IOS can support to automatically calculate metric for interface based on interface bandwidth.

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https://www.cisco.com/en/US/products/ps6599/products_white_paper09186a00800a3e6f.shtml

Default Metric

While some routing protocols calculate the link metric automatically  based on bandwidth (OSPF) or bandwidth/delay (Enhanced Interior Gateway  Routing Protocol [EIGRP]), there is no automatic calculation for IS-IS.

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Please check and help me to know what command if available used for above requirement.

Many Thanks& Regards,

Cuong,

[Nagendra Kumar Nainar · Accepted solution]

Hi Cuong,

ISIS interface cost is not dynamic like OSPF, it will be always 10 which can be maually changed by "isis metric" interface command.

Regards,

Nagendra

[lv_cuongvt]

Thanks for that,

Any road-map or change for this in future?

Regards,

Cuong,

[Giuseppe Larosa]

Hello Cuong,

no because it is the way ISIS has been specified not a Cisco implementation choice.

implementing auto cost would be a deviation from standards. Also ISIS on LAN interfaces allows to set different metric values for level-1 and level-2 and this would  make autocost complex.

What is important in real deployment is to enable wide metrics in order to be able to handle links of very different speeds

Setting the metric value(s) becomes part of configuring ISIS so it is not so cumbersome as it looks like

Hope to help

Giuseppe

[vkoyi85]

Hello,

The default metric of IS-IS protocol is 10 ,If you want to set it by yourself pls follow below configuration command and respective doc.

isis metric

To configure the value of an Intermediate System-to-Intermediate System (IS-IS) metric, use the isis metric command in interface configuration or subinterface mode. To restore the default metric value, use the no form of this command.

isis metric {metric-value | maximum} [level-1 | level-2]

no isis metric {metric-value | maximum} [level-1 | level-2]

Syntax Description

metric-value	Metric assigned to the link and used to calculate the cost from each other router via the links in the network to other destinations. You can configure this metric for Level 1 or Level 2 routing. The range is from 1to 16777214. The default value is 10.
maximum	Excludes a link or adjacency from the shortest path first (SPF) calculation.
level-1	(Optional) Specifies that this metric should be used only in the SPF calculation for Level 1 (intra-area) routing. If no optional keyword is specified, the metric is enabled on routing Level 1 and Level 2.
level-2	(Optional) Specifies that this metric should be used only in the SPF calculation for Level 2 (interarea) routing. If no optional keyword is specified, the metric is enabled on routing Level 1 and Level 2.

Command Default

The default metric value is set to 10.

Command Modes

Interface configuration
Subinterface configuration

Command History

Release	Modification
10.0	This command was introduced.
12.1	The maximum keyword was added.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.4(13)	The maximum keyword was made available under subinterface configuration mode.
12.4(13)T	The maximum keyword was made available under subinterface configuration mode.

Usage Guidelines

Specifying the level-1 or level-2 keyword resets the metric only for Level 1 or Level 2 routing, respectively.

We highly recommend that you configure metrics on all interfaces. If you do not do so, the IS-IS metrics are similar to hop-count metrics.

It is strongly recommended to use the metric-style wide command to configure IS-IS to use the new-style type, length, value (TLV) because TLVs that are used to advertise IPv4 information in link-state packets (LSPs) are defined to use only extended metrics. Cisco IOS software provides support of a 24-bit metric field, the so-called "wide metric." Using the new metric style, link metrics now have a maximum value of 16777214 with a total path metric of 4261412864.

Cisco IOS Release 12.4(13) and 12.4(13)T

Entering the maximum keyword will exclude the link from the SPF calculation. If a link is advertised with the maximum link metric, the link will not be considered during the normal SPF calculation. When the link is excluded from the SPF, it will not be advertised for calculating the normal SPF. An example would be a link that is available for traffic engineering, but not for hop-by-hop routing. If a link, such as one that is used for traffic engineering, should not be included in the SPF calculation, enter the isis metric command with the maximum keyword.

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Note The isis metric maximum command applies only when the metric-style wide command has been entered. The metric-style wide command is used to configure IS-IS to use the new-style TLV because TLVs that are used to advertise IPv4 information in link-state packets (LSPs) are defined to use only extended metrics.

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Examples

The following example configures serial interface 0 for a link-state metric cost of 15 for Level 1:

Router(config)# interface serial 0

Router(config-if)# isis metric 15 level-1

the following example sets the IS-IS metric for the link to maximum. SPF will ignore the link for both Level 1 and Level 2 routing because neither the level-1 keyword nor the level-2 keyword was entered.

Router(config)# interface fastethernet 0/0

Router(config-if)# isis metric maximum

Cisco IOS Release 12.4(13) and 12.4(13)T

The following example configures the isis metric maximum command on Ethernet subinterface 1/1.9.

Router(config)# interface Ethernet 1/1.9

Router(config-subif)# isis metric maximum

Related Commands

Command	Description
metric-style wide	Configures a router running IS-IS so that it generates and accepts only new-style TLVs.

If you have any doubts further Please look below command API for reference.

https://www.cisco.com/en/US/docs/ios/12_2/iproute/command/reference/1rfisis.html#wp1047780

Thanks & Regards,

Venkat Koyi

[lv_cuongvt]

Thanks all,

Regards,

Cuong,