--- 1/draft-ietf-roll-efficient-npdao-10.txt 2019-05-25 04:14:00.025056569 -0700 +++ 2/draft-ietf-roll-efficient-npdao-11.txt 2019-05-25 04:14:00.085058084 -0700 @@ -1,22 +1,22 @@ ROLL R. Jadhav, Ed. Internet-Draft Huawei Intended status: Standards Track P. Thubert -Expires: October 29, 2019 Cisco +Expires: November 26, 2019 Cisco R. Sahoo Z. Cao Huawei - April 27, 2019 + May 25, 2019 Efficient Route Invalidation - draft-ietf-roll-efficient-npdao-10 + draft-ietf-roll-efficient-npdao-11 Abstract This document describes the problems associated with No-Path Destination Advertisement Object (NPDAO) messaging used in Routing Protocol for Low power and lossy networks (RPL) for route invalidation and signaling changes to improve route invalidation efficiency. Status of This Memo @@ -27,21 +27,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on October 29, 2019. + This Internet-Draft will expire on November 26, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -50,59 +50,60 @@ include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language and Terminology . . . . . . . . . . 3 1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 4 1.3. Why NPDAO is important? . . . . . . . . . . . . . . . . . 5 - 2. Problems with current NPDAO messaging . . . . . . . . 6 + 2. Problems with current NPDAO messaging . . . . . . . . . . . . 6 2.1. Lost NPDAO due to link break to the previous parent . . . 6 2.2. Invalidate routes of dependent nodes . . . . . . . . . . 6 2.3. Possible route downtime caused by async operation of NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 6 3. Requirements for the NPDAO Optimization . . . . . . . . . . . 6 3.1. Req#1: Remove messaging dependency on link to the - previous parent . . . . . . . . . . . . . . . 6 + previous parent . . . . . . . . . . . . . . . . . . . . . 6 3.2. Req#2: Dependent nodes route invalidation on parent switching . . . . . . . . . . . . . . . . . . . . . . . . 7 3.3. Req#3: Route invalidation should not impact data traffic 7 4. Changes to RPL signaling . . . . . . . . . . . . . . . . . . 7 4.1. Change in RPL route invalidation semantics . . . . . . . 7 4.2. Transit Information Option changes . . . . . . . . . . . 8 4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 9 4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10 4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10 4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 10 - 4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 11 - 4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 12 + 4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK) . 10 + 4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 11 4.4. DCO Base Rules . . . . . . . . . . . . . . . . . . . . . 12 - 4.5. Other considerations . . . . . . . . . . . . . . . . . . 12 - 4.5.1. Dependent Nodes invalidation . . . . . . . . . . . . 12 - 4.5.2. NPDAO and DCO in the same network . . . . . . . . . . 13 - 4.5.3. DCO with multiple preferred parents . . . . . . . . . 13 - 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 - 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 + 4.5. Unsolicited DCO . . . . . . . . . . . . . . . . . . . . . 12 + 4.6. Other considerations . . . . . . . . . . . . . . . . . . 13 + 4.6.1. Dependent Nodes invalidation . . . . . . . . . . . . 13 + 4.6.2. NPDAO and DCO in the same network . . . . . . . . . . 13 + 4.6.3. DCO with multiple preferred parents . . . . . . . . . 14 + 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 6.1. New Registry for the Destination Cleanup Object (DCO) Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.2. New Registry for the Destination Cleanup Object - Acknowledgement (DCO-ACK) Status field . . . . . . . . . 15 + Acknowledgment (DCO-ACK) Status field . . . . . . . . . . 16 6.3. New Registry for the Destination Cleanup Object (DCO) - Acknowledgement Flags . . . . . . . . . . . . . . . . . . 16 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 - 8. Normative References . . . . . . . . . . . . . . . . . . . . 17 + Acknowledgment Flags . . . . . . . . . . . . . . . . . . 16 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 + 8. Normative References . . . . . . . . . . . . . . . . . . . . 18 Appendix A. Example Messaging . . . . . . . . . . . . . . . . . 18 A.1. Example DCO Messaging . . . . . . . . . . . . . . . . . . 18 A.2. Example DCO Messaging with multiple preferred parents . . 19 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 1. Introduction RPL [RFC6550] (Routing Protocol for Low power and lossy networks) specifies a proactive distance-vector based routing scheme. RPL has an optional messaging in the form of DAO (Destination Advertisement Object) messages, which the 6LBR (6Lo Border Router) and 6LR (6Lo Router) can use to learn a route towards the downstream nodes. In storing mode, DAO messages would result in routing entries being created on all intermediate 6LRs from the node's parent all the way @@ -313,71 +314,68 @@ In Figure 1, when node D decides to switch the path from B to C, it sends a regular DAO to node C with reachability information containing target as address of D and an incremented Path Sequence. Node C will update the routing table based on the reachability information in the DAO and in turn generate another DAO with the same reachability information and forward it to H. Node H also follows the same procedure as Node C and forwards it to node A. When node A receives the regular DAO, it finds that it already has a routing table entry on behalf of the target address of node D. It finds however that the next hop information for reaching node D has changed - i.e. node D has decided to change the paths. In this case, Node A + i.e., node D has decided to change the paths. In this case, Node A which is the common ancestor node for node D along the two paths (previous and new), should generate a DCO which traverses downwards in the network. 4.2. Transit Information Option changes Every RPL message is divided into base message fields and additional Options as described in Section 6 of [RFC6550]. The base fields apply to the message as a whole and options are appended to add message/use-case specific attributes. As an example, a DAO message may be attributed by one or more "RPL Target" options which specify the reachability information for the given targets. Similarly, a Transit Information option may be associated with a set of RPL Target options. This document specifies a change in the Transit Information Option to - contain the "Invalidate previous route" (I) bit. This I-bit signals - the common ancestor node to generate a DCO on behalf of the target - node. The I-bit is carried in the Transit Information Option which - augments the reachability information for a given set of RPL + contain the "Invalidate previous route" (I) flag. This I-flag + signals the common ancestor node to generate a DCO on behalf of the + target node. The I-flag is carried in the Transit Information Option + which augments the reachability information for a given set of RPL Target(s). Transit Information Option should be carried in the DAO - message with I-bit set in case route invalidation is sought for the + message with I-flag set in case route invalidation is sought for the corresponding target(s). 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x06 | Option Length |E|I| Flags | Path Control | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | Path Sequence | Path Lifetime | | - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + - | | - + + - | | - + Parent Address + - | | - + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | | + | Path Sequence | Path Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Updated Transit Information Option (New I flag added) - I (Invalidate previous route) bit: The 'I' flag is set by the target + I (Invalidate previous route) flag: The 'I' flag is set by the target node to indicate to the common ancestor node that it wishes to invalidate any previous route between the two paths. + [RFC6550] allows parent address to be sent in the Transit Information + Option depending on the mode of operation. In case of storing mode + of operation the field is usually not needed. In case of DCO, the + parent address field MUST not be included. + The common ancestor node SHOULD generate a DCO message in response to - this I-bit when it sees that the routing adjacencies have changed for - the target. I-bit governs the ownership of the DCO message in a way - that the target node is still in control of its own route + this I-flag when it sees that the routing adjacencies have changed + for the target. I-flag governs the ownership of the DCO message in a + way that the target node is still in control of its own route invalidation. 4.3. Destination Cleanup Object (DCO) A new ICMPv6 RPL control message type is defined by this specification called as "Destination Cleanup Object" (DCO), which is used for proactive cleanup of state and routing information held on behalf of the target node by 6LRs. The DCO message always traverses downstream and cleans up route information and other state information associated with the given target. @@ -445,36 +443,33 @@ options: 0x00 Pad1 0x01 PadN 0x05 RPL Target 0x06 Transit Information 0x09 RPL Target Descriptor The DCO carries an RPL Target Option and an associated Transit Information Option with a lifetime of 0x00000000 to indicate a loss - of reachability to that Target. The lifetime indicated in the - Transit Information Option of the DCO message MUST be set to - 0x00000000. + of reachability to that Target. 4.3.3. Path Sequence number in the DCO A DCO message may contain a Path Sequence in the Transit Information Option to identify the freshness of the DCO message. The Path Sequence in the DCO MUST use the same Path Sequence number present in the regular DAO message when the DCO is generated in response to a - DAO message. The Path Sequence present in the Transit Information - Option of the DAO and the correspondingly triggered DCO MUST be same. - Thus if a DCO is received by a 6LR and subsequently a DAO is received - with an old seqeunce number, then the DAO MUST be ignored. + DAO message. Thus if a DCO is received by a 6LR and subsequently a + DAO is received with an old seqeunce number, then the DAO MUST be + ignored. -4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) +4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK) The DCO-ACK message SHOULD be sent as a unicast packet by a DCO recipient in response to a unicast DCO message with 'K' flag set. If 'K' flag is not set then the receiver of the DCO message MAY send a DCO-ACK to signal an error condition. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RPLInstanceID |D| Reserved | DCOSequence | Status | @@ -530,82 +525,103 @@ same value as that of the DAO message in response to which the DCO is generated on the common ancestor node. 3. A node MAY set the 'K' flag in a unicast DCO message to solicit a unicast DCO-ACK in response in order to confirm the attempt. 4. A node receiving a unicast DCO message with the 'K' flag set SHOULD respond with a DCO-ACK. A node receiving a DCO message without the 'K' flag set MAY respond with a DCO-ACK, especially to report an error condition. 5. A node receiving a unicast DCO message MUST verify the stored Path Sequence in context to the given target. If the stored Path - Sequence is more fresh i.e. newer than the Path Sequence received - in the DCO, then the DCO MUST be dropped. + Sequence is more fresh i.e., newer than the Path Sequence + received in the DCO, then the DCO MUST be dropped. 6. A node that sets the 'K' flag in a unicast DCO message but does not receive DCO-ACK in response MAY reschedule the DCO message transmission for another attempt, up until an implementation specific number of retries. 7. A node receiving a unicast DCO message with its own address in the RPL Target Option MUST strip-off that Target Option. If this Target Option is the only one in the DCO message then the DCO message MUST be dropped. The scope of DCOSequence values is unique to each node. -4.5. Other considerations +4.5. Unsolicited DCO -4.5.1. Dependent Nodes invalidation + A 6LR may generate an unsolicited DCO to unilaterally cleanup the + path on behalf of the target entry. The 6LR has all the state + information namely, the Target address and the Path Sequence, + required for generating DCO in its routing table. The conditions why + 6LR may generate an unsolicited DCO is beyond the scope of this + document but some possible reasons could be: + + 1. On route expiry of an entry, a 6LR may decide to gracious cleanup + the entry by initiating DCO. + 2. 6LR needs to entertain higher priority entries in case the + routing table is full thus resulting in an eviction of existing + routing entry. In this case the eviction can be handled + graciously using DCO. + + Note that if the 6LR initiates a unilateral path cleanup using DCO + and if it has the latest state for the target then the DCO would + finally reach the target node. Thus the target node would be + informed of its invalidation. + +4.6. Other considerations + +4.6.1. Dependent Nodes invalidation Current RPL [RFC6550] does not provide a mechanism for route invalidation for dependent nodes. This document allows the dependent nodes invalidation. Dependent nodes will generate their respective DAOs to update their paths, and the previous route invalidation for those nodes should work in the similar manner described for switching - node. The dependent node may set the I-bit in the Transit + node. The dependent node may set the I-flag in the Transit Information Option as part of regular DAO so as to request invalidation of previous route from the common ancestor node. Dependent nodes do not have any indication regarding if any of its parent nodes in turn have decided to switch their parent. Thus for route invalidation the dependent nodes may choose to always set the - 'I' bit in all its DAO message's Transit Information Option. Note - that setting the I-bit is not counter productive even if there is no + 'I' flag in all its DAO message's Transit Information Option. Note + that setting the I-flag is not counter productive even if there is no previous route to be invalidated. -4.5.2. NPDAO and DCO in the same network +4.6.2. NPDAO and DCO in the same network Even with the changed semantics, the current NPDAO mechanism in [RFC6550] can still be used, for example, when the route lifetime expiry of the target happens or when the node simply decides to gracefully terminate the RPL session on graceful node shutdown. Moreover a deployment can have a mix of nodes supporting the DCO and the existing NPDAO mechanism. It is also possible that the same node - supports both the NPDAO and DCO signalling. + supports both the NPDAO and DCO signaling. Section 9.8 of [RFC6550] states, "When a node removes a node from its DAO parent set, it SHOULD send a No-Path DAO message to that removed DAO parent to invalidate the existing router". This document introduces an alternate and more optimized way of route invalidation but it also allows existing NPDAO messaging to work. Thus an implementation has two choices to make when a route invalidation is to be initiated: 1. Use NPDAO to invalidate the previous route and send regular DAO on the new path. - 2. Send regular DAO on the new path with the 'I' bit set in the + 2. Send regular DAO on the new path with the 'I' flag set in the Transit Information Option such that the common ancestor node initiates the DCO message downstream to invalidate the previous route. This document recommends using option 2 for reasons specified in Section 3 in this document. -4.5.3. DCO with multiple preferred parents +4.6.3. DCO with multiple preferred parents [RFC6550] allows a node to select multiple preferred parents for route establishment. Section 9.2.1 of [RFC6550] specifies, "All DAOs generated at the same time for the same Target MUST be sent with the same Path Sequence in the Transit Information". Subsequently when route invalidation has to be initiated, RPL mentions use of NPDAO which can be initiated with an updated Path Sequence to all the parent nodes through which the route is to be invalidated. With DCO, the Target node itself does not initiate the route @@ -624,75 +640,80 @@ This documents recommends using a DelayDCO timer value of 1sec. This value is inspired by the default DelayDAO value of 1sec in [RFC6550]. Here the hypothesis is that the DAOs from all possible parent set would be received on the common ancestor within this time period. Note that there is no requirement of synchronization between DCO and DAOs. The DelayDCO timer simply ensures that the DCO control overhead can be reduced and is only needed when the network contains nodes using multiple preferred parent. -5. Acknowledgements +5. Acknowledgments Many thanks to Alvaro Retana, Cenk Gundogan, Simon Duquennoy, Georgios Papadopoulous, Peter Van Der Stok for their review and comments. Alvaro Retana helped shape this document's final version with critical review comments. 6. IANA Considerations IANA is requested to allocate new codes for the DCO and DCO-ACK messages from the RPL Control Codes registry. +------+---------------------------------------------+--------------+ | Code | Description | Reference | +------+---------------------------------------------+--------------+ | TBD1 | Destination Cleanup Object | This | | | | document | - | TBD2 | Destination Cleanup Object Acknowledgement | This | + | TBD2 | Destination Cleanup Object Acknowledgment | This | | | | document | | TBD3 | Secure Destination Cleanup Object | This | | | | document | | TBD4 | Secure Destination Cleanup Object | This | - | | Acknowledgement | document | + | | Acknowledgment | document | +------+---------------------------------------------+--------------+ + IANA is requested to allocate bit 1 from the Transit Information - Option Flags registry for the I-bit (Section 4.2) + Option Flags registry for the I-flag (Section 4.2) 6.1. New Registry for the Destination Cleanup Object (DCO) Flags - IANA has created a registry for the 8-bit Destination Cleanup Object - (DCO) Flags field. + IANA is requested to create a registry for the 8-bit Destination + Cleanup Object (DCO) Flags field. This registry should be located in + existing category of "Routing Protocol for Low Power and Lossy + Networks (RPL)". New bit numbers may be allocated only by an IETF Review. Each bit is tracked with the following qualities: oBit number (counting from bit 0 as the most significant bit) oCapability description oDefining RFC The following bits are currently defined: +------------+------------------------------+---------------+ | Bit number | Description | Reference | +------------+------------------------------+---------------+ | 0 | DCO-ACK request (K) | This document | | 1 | DODAGID field is present (D) | This document | +------------+------------------------------+---------------+ DCO Base Flags -6.2. New Registry for the Destination Cleanup Object Acknowledgement +6.2. New Registry for the Destination Cleanup Object Acknowledgment (DCO-ACK) Status field - IANA has created a registry for the 8-bit Destination Cleanup Object - Acknowledgement (DCO-ACK) Status field. + IANA is requested to create a registry for the 8-bit Destination + Cleanup Object Acknowledgment (DCO-ACK) Status field. This registry + should be located in existing category of "Routing Protocol for Low + Power and Lossy Networks (RPL)". New Status values may be allocated only by an IETF Review. Each value is tracked with the following qualities: oStatus Code oDescription oDefining RFC The following bits are currently defined: @@ -702,24 +723,26 @@ +------------+----------------------------------------+-------------+ | 0 | Unqualified acceptance | This | | | | document | | 1 | No routing-entry for the indicated | This | | | Target found | document | +------------+----------------------------------------+-------------+ DCO Status Codes 6.3. New Registry for the Destination Cleanup Object (DCO) - Acknowledgement Flags + Acknowledgment Flags - IANA has created a registry for the 8-bit Destination Cleanup Object - (DCO) Acknowledgement Flags field. + IANA is requested to create a registry for the 8-bit Destination + Cleanup Object (DCO) Acknowledgment Flags field. This registry + should be located in existing category of "Routing Protocol for Low + Power and Lossy Networks (RPL)". New bit numbers may be allocated only by an IETF Review. Each bit is tracked with the following qualities: oBit number (counting from bit 0 as the most significant bit) oCapability description oDefining RFC The following bits are currently defined: @@ -728,51 +751,63 @@ +------------+------------------------------+---------------+ | 0 | DODAGID field is present (D) | This document | +------------+------------------------------+---------------+ DCO-ACK Base Flags 7. Security Considerations This document introduces the ability for a common ancestor node to invalidate a route on behalf of the target node. The common ancestor - node is directed to do so by the target node using the 'I' bit in + node is directed to do so by the target node using the 'I' flag in DCO's Transit Information Option. However, the common ancestor node is in a position to unilaterally initiate the route invalidation - since it possesses all the required state information namely, the - Target address and the correspond Path Sequence. Thus a rogue common - ancestor node could initiate such an invalidation and impact the - traffic to the target node. This document assumes that the security - mechanisms as defined in [RFC6550] are followed, which means that the - common ancestor node is part of the RPL network because it has the - required credentials. + since it possesses all the required state information, namely, the + Target address and the corresponding Path Sequence. Thus a rogue + common ancestor node could initiate such an invalidation and impact + the traffic to the target node. + + This document also introduces an I-flag which is set by the target + node and used by the ancestor node to initiate a DCO if the ancestor + nodes sees an update in the route adjacency. However, this flag + could be spoofed by a malicious 6LR in the path and can cause + invalidation of an existing active path. Note that invalidation will + happen only if the other conditions such as Path Sequence condition + is also met. Having said that a malicious 6LR may spoof a DAO on + behalf of the (sub) child with the I-flag set and can cause route + invalidation on behalf of the (sub) child node. + + This document assumes that the security mechanisms as defined in + [RFC6550] are followed, which means that the common ancestor node and + all the 6LRs are part of the RPL network because they have the + required credentials. A non-secure RPL network needs to take into + consideration the risks highlighted in this section. All RPL messages support a secure version of messages which allows integrity protection using either a MAC or a signature. Optionally, secured RPL messages also have encryption protection for confidentiality. The document adds new messages (DCO, DCO-ACK) which are syntactically similar to existing RPL messages such as DAO, DAO-ACK. Secure versions of DCO and DCO-ACK are added similar to other RPL messages (such as DAO, DAO-ACK). RPL supports three security modes as mentioned in Section 10.1 of [RFC6550]: 1. Unsecured: In this mode, it is expected that the RPL control messages are secured by other security mechanisms, such as link- layer security. In this mode, the RPL control messages, - including DCO, DCO-ACK, do not have Security sections. A DCO and - DCO-ACK message which is not encrypted at link-layer MUST not be - handled by the RPL layer. Also all the DCO and DCO-ACK messages - that are transmitted MUST be link-layer encrypted. + including DCO, DCO-ACK, do not have Security sections. Also note + that unsecured mode does not imply that all messages are sent + without any protection. 2. Preinstalled: In this mode, RPL uses secure messages. Thus secure versions of DCO, DCO-ACK MUST be used in this mode. 3. Authenticated: In this mode, RPL uses secure messages. Thus secure versions of DCO, DCO-ACK MUST be used in this mode. 8. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, @@ -794,26 +829,27 @@ A.1. Example DCO Messaging In Figure 1, node (D) switches its parent from (B) to (C). This example assumes that Node D has already established its own route via Node B-G-A-6LBR using pathseq=x. The example uses DAO and DCO messaging convention and specifies only the required parameters to explain the example namely, the parameter 'tgt', which stands for Target Option and value of this parameter specifies the address of the target node. The parameter 'pathseq', which specifies the Path Sequence value carried in the Transit Information Option. The - parameter 'I_flag' specifies the 'I' bit in the Transit Information + parameter 'I_flag' specifies the 'I' flag in the Transit Information Option. sequence of actions is as follows: 1. Node D switches its parent from node B to node C 2. D sends a regular DAO(tgt=D,pathseq=x+1,I_flag=1) in the updated path to C + 3. C checks for a routing entry on behalf of D, since it cannot find an entry on behalf of D it creates a new routing entry and forwards the reachability information of the target D to H in a DAO(tgt=D,pathseq=x+1,I_flag=1). 4. Similar to C, node H checks for a routing entry on behalf of D, cannot find an entry and hence creates a new routing entry and forwards the reachability information of the target D to A in a DAO(tgt=D,pathseq=x+1,I_flag=1). 5. Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1), and checks for a routing entry on behalf of D. It finds a routing entry but @@ -810,21 +846,21 @@ 3. C checks for a routing entry on behalf of D, since it cannot find an entry on behalf of D it creates a new routing entry and forwards the reachability information of the target D to H in a DAO(tgt=D,pathseq=x+1,I_flag=1). 4. Similar to C, node H checks for a routing entry on behalf of D, cannot find an entry and hence creates a new routing entry and forwards the reachability information of the target D to A in a DAO(tgt=D,pathseq=x+1,I_flag=1). 5. Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1), and checks for a routing entry on behalf of D. It finds a routing entry but - checks that the next hop for target D is different (i.e. Node + checks that the next hop for target D is different (i.e., Node G). Node A checks the I_flag and generates DCO(tgt=D,pathseq=x+1) to previous next hop for target D which is G. Subsequently, Node A updates the routing entry and forwards the reachability information of target D upstream DAO(tgt=D,pathseq=x+1,I_flag=1). 6. Node G receives the DCO(tgt=D,pathseq=x+1). It checks if the received path sequence is latest as compared to the stored path sequence. If it is latest, Node G invalidates routing entry of target D and forwards the (un)reachability information downstream to B in DCO(tgt=D,pathseq=x+1). @@ -932,13 +967,13 @@ Bangalore, Karnataka 560037 India Phone: +91-080-49160700 Email: rabinarayans@huawei.com Zhen Cao Huawei W Chang'an Ave Beijing - China + P.R. China Email: zhencao.ietf@gmail.com