draft-ietf-idr-aigp-13.txt		draft-ietf-idr-aigp-14.txt
	Network Working Group Pradosh Mohapatra		Network Working Group Pradosh Mohapatra
	Internet Draft Cumulus Networks		Internet Draft Cumulus Networks
	Intended Status: Proposed Standard		Intended Status: Proposed Standard
	Expires: June 3, 2014 Rex Fernando		Expires: June 16, 2014 Rex Fernando
	Eric C. Rosen		Eric C. Rosen
	Cisco Systems, Inc.		Cisco Systems, Inc.
	James Uttaro		James Uttaro
	ATT		ATT
	December 3, 2013		December 16, 2013
	The Accumulated IGP Metric Attribute for BGP		The Accumulated IGP Metric Attribute for BGP
	draft-ietf-idr-aigp-13.txt		draft-ietf-idr-aigp-14.txt
	Abstract		Abstract
	Routing protocols that have been designed to run within a single		Routing protocols that have been designed to run within a single
	administrative domain ("IGPs") generally do so by assigning a metric		administrative domain ("IGPs") generally do so by assigning a metric
	to each link, and then choosing as the installed path between two		to each link, and then choosing as the installed path between two
	nodes the path for which the total distance (sum of the metric of		nodes the path for which the total distance (sum of the metric of
	each link along the path) is minimized. BGP, designed to provide		each link along the path) is minimized. BGP, designed to provide
	routing over a large number of independent administrative domains		routing over a large number of independent administrative domains
	("autonomous systems"), does not make its path selection decisions		("autonomous systems"), does not make its path selection decisions
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	3.1 Applicability Restrictions and Cautions ............... 6		3.1 Applicability Restrictions and Cautions ............... 6
	3.2 Handling a Malformed AIGP Attribute ................... 6		3.2 Handling a Malformed AIGP Attribute ................... 6
	3.3 Restrictions on Sending/Receiving ..................... 7		3.3 Restrictions on Sending/Receiving ..................... 7
	3.4 Creating and Modifying the AIGP Attribute ............. 7		3.4 Creating and Modifying the AIGP Attribute ............. 7
	3.4.1 Originating the AIGP Attribute ........................ 7		3.4.1 Originating the AIGP Attribute ........................ 7
	3.4.2 Modifications by the Originator ....................... 9		3.4.2 Modifications by the Originator ....................... 9
	3.4.3 Modifications by a Non-Originator ..................... 9		3.4.3 Modifications by a Non-Originator ..................... 9
	4 Decision Process ...................................... 11		4 Decision Process ...................................... 11
	4.1 When a Route has an AIGP Attribute .................... 11		4.1 When a Route has an AIGP Attribute .................... 11
	4.2 When the Route to the Next Hop has an AIGP attribute .. 12		4.2 When the Route to the Next Hop has an AIGP attribute .. 12
	5 Deployment Considerations ............................. 12		5 Deployment Considerations ............................. 13
	6 IANA Considerations ................................... 13		6 IANA Considerations ................................... 13
	7 Security Considerations ............................... 13		7 Security Considerations ............................... 13
	8 Acknowledgments ....................................... 13		8 Acknowledgments ....................................... 13
	9 Authors' Addresses .................................... 13		9 Authors' Addresses .................................... 14
	10 Normative References .................................. 14		10 Normative References .................................. 14
	11 Informative References ................................ 14		11 Informative References ................................ 14
	1. Specification of requirements		1. Specification of requirements
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].		document are to be interpreted as described in [RFC2119].
	2. Introduction		2. Introduction
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	- Accumulated IGP Metric.		- Accumulated IGP Metric.
	The value field of the AIGP TLV is always 8 bytes long. IGP		The value field of the AIGP TLV is always 8 bytes long. IGP
	metrics are frequently expressed as 4-octet values, and this		metrics are frequently expressed as 4-octet values, and this
	ensures that the AIGP attribute can be used to hold the sum of an		ensures that the AIGP attribute can be used to hold the sum of an
	arbitrary number of 4-octet values.		arbitrary number of 4-octet values.
	When an AIGP attribute is created, it SHOULD contain no more than one		When an AIGP attribute is created, it SHOULD contain no more than one
	AIGP TLV. However, if it contains more than one AIGP TLV, only the		AIGP TLV. However, if it contains more than one AIGP TLV, only the
	first one is is used as described in Section 3.4 and Section 4. In		first one is used as described in Section 3.4 and Section 4. In the
	the remainder of this document, we will use the term "value of the		remainder of this document, we will use the term "value of the AIGP
	AIGP TLV" to mean the value of the first AIGP TLV in the AIGP		TLV" to mean the value of the first AIGP TLV in the AIGP attribute.
	attribute. Any other AIGP TLVs in the AIGP attribute MUST be passed		Any other AIGP TLVs in the AIGP attribute MUST be passed along
	along unchanged if the AIGP attribute is passed along.		unchanged if the AIGP attribute is passed along.
	3.1. Applicability Restrictions and Cautions		3.1. Applicability Restrictions and Cautions
	This document only considers the use of the AIGP attribute in		This document only considers the use of the AIGP attribute in
	networks where each router uses tunneling of some sort to deliver a		networks where each router uses tunneling of some sort to deliver a
	packet to its BGP next hop. Use of the AIGP attribute in networks		packet to its BGP next hop. Use of the AIGP attribute in networks
	that do not use tunneling is outside the scope of this document.		that do not use tunneling is outside the scope of this document.
	If a Route Reflector supports the AIGP attribute, but some of its		If a Route Reflector supports the AIGP attribute, but some of its
	clients do not, then the routing choices that result may not all		clients do not, then the routing choices that result may not all
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	- The default value of AIGP_SESSION, for IBGP and confederation-		- The default value of AIGP_SESSION, for IBGP and confederation-
	EBGP sessions, SHOULD be "enabled."		EBGP sessions, SHOULD be "enabled."
	The AIGP attribute MUST NOT be sent on any BGP session for which		The AIGP attribute MUST NOT be sent on any BGP session for which
	AIGP_SESSION is disabled.		AIGP_SESSION is disabled.
	If an AIGP attribute is received on a BGP session for which		If an AIGP attribute is received on a BGP session for which
	AIGP_SESSION is disabled, the attribute MUST be treated exactly as if		AIGP_SESSION is disabled, the attribute MUST be treated exactly as if
	it were an unrecognized non-transitive attribute. That is, "it MUST		it were an unrecognized non-transitive attribute. That is, "it MUST
	be quietly ignored and not passed along to other BGP peers" (see		be quietly ignored and not passed along to other BGP peers" (see
	[BGP], section 5).		[BGP], section 5). However, the fact that the attribute was received
			SHOULD be logged (in a rate-limited manner).
	3.4. Creating and Modifying the AIGP Attribute		3.4. Creating and Modifying the AIGP Attribute
	3.4.1. Originating the AIGP Attribute		3.4.1. Originating the AIGP Attribute
	An implementation that supports the AIGP attribute MUST support a		An implementation that supports the AIGP attribute MUST support a
	configuration item, AIGP_ORIGINATE, that enables or disables its		configuration item, AIGP_ORIGINATE, that enables or disables its
	creation and attachment to routes. The default value of		creation and attachment to routes. The default value of
	AIGP_ORIGINATE MUST be "disabled".		AIGP_ORIGINATE MUST be "disabled".
	A BGP speaker MUST NOT add the AIGP attribute to any route whose path		A BGP speaker MUST NOT add the AIGP attribute to any route whose path
	leads outside the "AIGP administrative domain" to which the BGP		leads outside the "AIGP administrative domain" to which the BGP
	speaker belongs. It may be added only to routes that satisfy one of		speaker belongs. It may be added only to routes that satisfy one of
	the following conditions:		the following conditions:
	- The route is a static route that is being redistributed into BGP		- The route is a static route that is being redistributed into BGP;
	- The route is an IGP route that is being redistributed into BGP		- The route is an IGP route that is being redistributed into BGP;
	- The route is an IBGP-learned route whose AS_PATH attribute is		- The route is an IBGP-learned route whose AS_PATH attribute is
	empty.		empty;
	- The route is an EBGP-learned route whose AS_PATH contains only		- The route is an EBGP-learned route whose AS_PATH contains only
	ASes that are in the same AIGP Administrative Domain as the BGP		ASes that are in the same AIGP Administrative Domain as the BGP
	speaker.		speaker.
	A BGP speaker R MUST NOT add the AIGP attribute to any route for		A BGP speaker R MUST NOT add the AIGP attribute to any route for
	which R does not set itself as the next hop.		which R does not set itself as the next hop.
	It SHOULD be possible to set AIGP_ORIGINATE to "enabled for the		It SHOULD be possible to set AIGP_ORIGINATE to "enabled for the
	routes of a particular IGP that are redistributed into BGP" (where "a		routes of a particular IGP that are redistributed into BGP" (where "a
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	that R1 is about to redistribute that route on a BGP session that is		that R1 is about to redistribute that route on a BGP session that is
	enabled for sending/receiving the attribute.		enabled for sending/receiving the attribute.
	If R1 does not change the Next Hop of the route, then R1 MUST NOT		If R1 does not change the Next Hop of the route, then R1 MUST NOT
	change the AIGP attribute value of the route.		change the AIGP attribute value of the route.
	In all the computations discussed in this section, the AIGP value		In all the computations discussed in this section, the AIGP value
	MUST be capped at its maximum unsigned value 0xffffffffffffffff.		MUST be capped at its maximum unsigned value 0xffffffffffffffff.
	Increasing the AIGP value MUST NOT cause the value to wrap around.		Increasing the AIGP value MUST NOT cause the value to wrap around.
	If R1 changes the Next Hop of the route from R2 to R1, and if R1's		Suppose R1 changes the Next Hop of the route from R2 to R1. If R1's
	route to R2 is an IGP-learned route, or a static route that does not		route to R2 is either (a) an IGP-learned route or (b) a static route
	require recursive next hop resolution, then R1 MUST increase the		that does not require recursive next hop resolution, then R1 MUST
	value of the AIGP TLV by adding to A the distance from R1 to R2.		increase the value of the AIGP TLV by adding to A the distance from
	This distance is either the IGP-computed distance from R1 to R2, or		R1 to R2. This distance is either the IGP-computed distance from R1
	some value determined by policy. However, A MUST be increased by a		to R2, or some value determined by policy. However, A MUST be
	non-zero amount.		increased by a non-zero amount.
	Note that if R1 and R2 above are EBGP neighbors, and there is a		It is possible that R1 and R2 above are EBGP neighbors, and that
	direct link between them on which no IGP is running, then when R1		there is a direct link between them on which no IGP is running. Then
	changes the next hop of a route from R2 to R1, the AIGP TLV value		when R1 changes the next hop of a route from R2 to R1, the AIGP TLV
	MUST be increased by a non-zero amount. The amount of the increase		value MUST be increased by a non-zero amount. The amount of the
	SHOULD be such that it is properly comparable to the IGP metrics.		increase SHOULD be such that it is properly comparable to the IGP
	E.g., if the IGP metric is a function of latency, then the amount of		metrics. E.g., if the IGP metric is a function of latency, then the
	the increase should be a function of the latency from R1 to R2.		amount of the increase should be a function of the latency from R1 to
			R2.
			Suppose R1 changes the Next Hop of the route from R2 to R1, and R1's
			route to R2 is either (a) a BGP-learned route or (b) a static route
			that requires recursive next hop resolution. Then the AIGP TLV value
			needs to be increased in several steps, according to the following
			procedure. (Note that this procedure is ONLY used when recursive
			next hop resolution is needed.)
	If R1 changes the Next Hop of the route from R2 to R1, and if R1's
	route to R2 is a BGP-learned route, or a static route that requires
	recursive next hop resolution, then the AIGP TLV value needs to be
	increased in several steps, according to the following procedure.
	(Note that this procedure is ONLY used when recursive next hop
	resolution is needed.)
	1. Let Xattr be the new AIGP TLV value.		1. Let Xattr be the new AIGP TLV value.
	2. Initialize Xattr to A.		2. Initialize Xattr to A.
	3. Set the XNH to R2.		3. Set the XNH to R2.
	4. Find the route to XNH.		4. Find the route to XNH.
	5. If the route to XNH does not require recursive next hop		5. If the route to XNH does not require recursive next hop
	resolution, get the distance D from R1 to XNH. (Note that this		resolution, get the distance D from R1 to XNH. (Note that this
	condition cannot be satisfied the first time through this		condition cannot be satisfied the first time through this
	procedure.) If D is above a configurable threshold, set the		procedure.) If D is above a configurable threshold, set the
	AIGP TLV value to Xattr+D. If D is below a configurable		AIGP TLV value to Xattr+D. If D is below a configurable
	threshold, set the AIGP TLV value to Xattr. In either case,		threshold, set the AIGP TLV value to Xattr. In either case,
	exit this procedure.		exit this procedure.
	6. If the route to XNH is a BGP-learned route, and the route does		6. If the route to XNH is a BGP-learned route that does NOT have
	NOT have an AIGP attribute, then exit this procedure and do not		an AIGP attribute, then exit this procedure and do not pass on
	pass on any AIGP attribute. If the route has an AIGP attribute		any AIGP attribute. If the route has an AIGP attribute without
	without an AIGP TLV, then the AIGP attribute MAY be passed		an AIGP TLV, then the AIGP attribute MAY be passed along
	along unchanged.		unchanged.
	7. If the route to XNH is a BGP-learned route, and the route has		7. If the route to XNH is a BGP-learned route that has an AIGP TLV
	an AIGP TLV value of Y, then set Xattr=Xattr+Y, and set XNH to		value of Y, then set Xattr=Xattr+Y and set XNH to the next hop
	the next hop of this route. (The intention here is that Y is		of this route. (The intention here is that Y is the AIGP TLV
	the AIGP TLV value of the route as it was received by R1,		value of the route as it was received by R1, without having
	without having been modified by R1.)		been modified by R1.)
	8. Go to step 4.		8. Go to step 4.
	The AIGP TLV value of a given route depends on (a) the AIGP TLV		The AIGP TLV value of a given route depends on (a) the AIGP TLV
	values of all the next hops that are recursively resolved during this		values of all the next hops that are recursively resolved during this
	procedure, and (b) the IGP distance to any next hop that is not		procedure, and (b) the IGP distance to any next hop that is not
	recursively resolved. Any change due to (a) in any of these values		recursively resolved. Any change due to (a) in any of these values
	MUST trigger a new AIGP computation for that route. Whether a change		MUST trigger a new AIGP computation for that route. Whether a change
	due to (b) triggers a new AIGP computation depends upon whether the		due to (b) triggers a new AIGP computation depends upon whether the
	change in IGP distance exceeds a configurable threshold.		change in IGP distance exceeds a configurable threshold.
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	- neither of the two routes has an AIGP attribute containing an		- neither of the two routes has an AIGP attribute containing an
	AIGP TLV.		AIGP TLV.
	The BGP decision process as specified in [BGP] makes use, in its tie		The BGP decision process as specified in [BGP] makes use, in its tie
	breaker procedures, of "interior cost", defined as follows:		breaker procedures, of "interior cost", defined as follows:
	"interior cost of a route is determined by calculating the metric		"interior cost of a route is determined by calculating the metric
	to the NEXT_HOP for the route using the Routing Table."		to the NEXT_HOP for the route using the Routing Table."
	Suppose route T has a next hop of N. We modify the notion of the		This document replaces the "interior cost" tie breaker of [BGP] with
	"interior cost" from node R1 to node N as follows:		a tie breaker based on the "AIGP-enhanced interior cost". Suppose
			route T has a next hop of N. The "AIGP-enhanced interior cost" from
			node R1 to node N is defined as follows:
	- Let R2 be the BGP next hop of the route to N, after all recursive		- Let R2 be the BGP next hop of the route to N after all recursive
	resolution of the next hop is done. Let m be the IGP distance		resolution of the next hop is done. Let m be the IGP distance
	(or in the case of a static route, the configured distance) from		(or in the case of a static route, the configured distance) from
	R1 to R2.		R1 to R2.
	- If the installed route to N has an AIGP attribute with an AIGP		- If the installed route to N has an AIGP attribute with an AIGP
	TLV, set A to the AIGP value of the route to N, computing the		TLV, set A to its AIGP TLV value, computed according to the
	AIGP value of the route according to the procedure of section		procedure of section 3.4.3.
	3.4.3.
	- If the installed route to N does not have an AIGP value, set A to		- If the installed route to N does not have an AIGP attribute with
	0.		an AIGP TLV, set A to 0.
	- The "interior cost" of route T is the quantity A+m.		- The "AIGP-enhanced interior cost" of route T is the quantity A+m.
			The "interior cost" tie breaker of [BGP] is then applied, but using
			the "AIGP-enhanced interior cost" instead of the "interior cost" as
			defined in [BGP].
	5. Deployment Considerations		5. Deployment Considerations
	Using the AIGP attribute to achieve a desired routing policy will be		Using the AIGP attribute to achieve a desired routing policy will be
	more effective if each BGP speaker can use it to choose from among		more effective if each BGP speaker can use it to choose from among
	multiple routes. Thus is it highly recommended that the procedures of		multiple routes. Thus is it highly recommended that the procedures of
	[BESTEXT] and [ADD-PATH] be used in conjunction with the AIGP		[BESTEXT] and [ADD-PATH] be used in conjunction with the AIGP
	Attribute.		Attribute.
	If a Route Reflector does not pass all paths to its clients, then it		If a Route Reflector does not pass all paths to its clients, then it
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	desired.		desired.
	Improper configuration on both ends of an EBGP connection could		Improper configuration on both ends of an EBGP connection could
	result in an AIGP attribute being passed from one service provider to		result in an AIGP attribute being passed from one service provider to
	another. This would likely result in an unsound selection of paths.		another. This would likely result in an unsound selection of paths.
	8. Acknowledgments		8. Acknowledgments
	The authors would like to thank Waqas Alam, Rajiv Asati, Bruno		The authors would like to thank Waqas Alam, Rajiv Asati, Bruno
	Decraene, Brian Dickson, Clarence Filsfils, Anoop Kapoor, Pratima		Decraene, Brian Dickson, Clarence Filsfils, Anoop Kapoor, Pratima
	Kini, Thomas Mangin, Robert Raszuk, Yakov Rekhter, Eric Rosenberg,		Kini, Sue Hares, Thomas Mangin, Robert Raszuk, Yakov Rekhter, Eric
	Samir Saad, John Scudder, Shyam Sethuram, and Ilya Varlashkin for		Rosenberg, Samir Saad, John Scudder, Shyam Sethuram, and Ilya
	their input.		Varlashkin for their input.
	9. Authors' Addresses		9. Authors' Addresses
	Rex Fernando		Rex Fernando
	Cisco Systems, Inc.		Cisco Systems, Inc.
	170 Tasman Drive		170 Tasman Drive
	San Jose, CA 95134		San Jose, CA 95134
	Email: rex@cisco.com		Email: rex@cisco.com
	Pradosh Mohapatra		Pradosh Mohapatra
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