Re: [Bier] Questions regarding <draft-zhang-bier-bierin6-03>

Xiejingrong <xiejingrong@huawei.com> Fri, 12 July 2019 23:34 UTC

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From: Xiejingrong <xiejingrong@huawei.com>
To: "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net>, Antoni Przygienda <prz@juniper.net>, "draft-zhang-bier-bierin6@ietf.org" <draft-zhang-bier-bierin6@ietf.org>, BIER WG <bier@ietf.org>
Thread-Topic: Questions regarding <draft-zhang-bier-bierin6-03>
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Date: Fri, 12 Jul 2019 23:33:51 +0000
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Subject: Re: [Bier] Questions regarding <draft-zhang-bier-bierin6-03>
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Hi Jeffrey,
Please see my comments inline below
________________________________
发件人: Jeffrey (Zhaohui) Zhang [zzhang@juniper.net]
发送时间: 2019年7月12日 22:27
收件人: Xiejingrong; Antoni Przygienda; draft-zhang-bier-bierin6@ietf.org; BIER WG
主题: RE: Questions regarding <draft-zhang-bier-bierin6-03>

I don’t have a good understanding about the writing in the latest email below, but for the following original comment that led to it:


  *   [XJR Q6]: You have to walk the ext header chain and get the last NH to judge if this packet need to be discard, right? For example for an incoming packet(ipv6hdr+RoutingHeader+DestOptHdr<nh!=TBD>), you have to walk the whole extension header chain until you know the last NH, to execute the above “discard” action. Right?


What is the problem with that? This document is saying that for BIER packets, the only header that is expected is the TBD (for BIER) and otherwise you drop it. Normally, you would not have the (ipv6hdr+RoutingHeader+DestOptHdr<nh!=TBD>) situation.
 [XJR]  This document also said the following.
   Any IPv6 packet arriving on BFRs and BFERs, with
   multiple extension header where the last extension header has a Next
   Header field set to TBD, SHOULD be discard and the node should
   transmit an ICMP Parameter Problem message to the source of the
   packet (BFIR) with an ICMP code value of TBD10 ('invalid options for
   BIERin6').

If the concern is that someone could maliciously inject that kind of packets for the purpose of slowing down a targeted BFR, then any of the following situation in RFC8200, independent of BIER, will have the same effect:
[XJR] Right. There is also concern of injection of packets to slow down a targeted BFR. That may not the below case listed in RFC8200.
Also, there are concerns of flexibility as my comments before.
For example:
BIER may want to process a packet with IPv6 NH=BIER in fast-path, and drop IPv6 NH=xxx and Last_NH=BIER.
BIER may want to process a packet with IPv6 NH=BIER or IPv6 NH=RH and RH_NH=BIER in fast-path, and drop IPv6 NH=xxx and Last_NH=BIER.
a new feature, let's say REIB may have the similar requirements:
REIB may want to process a packet with IPv6 NH=REIB in fast-path, and drop IPv6 NH=xxx and Last_NH=REIB.
REIB may want to process a packet with IPv6 NH=REIB or IPv6 NH=RH and RH_NH=REIB in fast-path, and drop IPv6 NH=xxx and Last_NH=REIB.
then I guess a lot of "walking through the EH chain" have to be executed like [XJR Q8].

Thanks,
Jingrong

   If, as a result of processing a header, the destination node is
   required to proceed to the next header but the Next Header value in
   the current header is unrecognized by the node, it should discard the
   packet and send an ICMP Parameter Problem message to the source of
   the packet, with an ICMP Code value of 1 ("unrecognized Next Header
   type encountered") and the ICMP Pointer field containing the offset
   of the unrecognized value within the original packet.  The same
   action should be taken if a node encounters a Next Header value of
   zero in any header other than an IPv6 header.

Jeffrey


From: Xiejingrong <xiejingrong@huawei.com>
Sent: Friday, July 12, 2019 7:20 AM
To: Antoni Przygienda <prz@juniper.net>et>; Jeffrey (Zhaohui) Zhang <zzhang@juniper.net>et>; draft-zhang-bier-bierin6@ietf.org; BIER WG <bier@ietf.org>
Subject: RE: Questions regarding <draft-zhang-bier-bierin6-03>

Hi Tony,

Exactly, the whole v6 extension headers(EH) and the v6 options consideration is basically a first stab!

Once a judgement is based on the “Upper-layer Protocol”, the last next header of a chain, then a walk through the chain is unavoidable, to “dig out” the right format that need to be processed in fast-path.

The difficulty with a “regular” IPv6 DA is that, normal things like TCP/UDP/ICMPv6 packet must be handled without much impact on it.

Use a “XXX specific IPv6 DA” is not only the SRv6-NetworkProgramming concept, but also the ISO NSAP address as I learned from a book and found in the WIKI https://en.wikipedia.org/wiki/NSAP_address<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_NSAP-5Faddress&d=DwMFAg&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=f7wsLGcfzAWDNS6XNTBZwj_OLAOsZZqdrR2IDAzeZqE&m=hKlg11Qzoo3dyO4pZGNb6wtU4M6Kb1RXIFHB6JnSl4A&s=Rh1tyYzDzhRq7ymA_JEJduNT94j_xiGhiQ-QgbwQ9L4&e=>94j_xiGhiQ-QgbwQ9L4&e=>:

The NSEL (Network-Selector) is a field in the NSAP address that identifies the network layer<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Network-5Flayer&d=DwMFAg&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=f7wsLGcfzAWDNS6XNTBZwj_OLAOsZZqdrR2IDAzeZqE&m=hKlg11Qzoo3dyO4pZGNb6wtU4M6Kb1RXIFHB6JnSl4A&s=CseHsrq8z_Cjx0ZsXzuYT3X9_3CMLv4SkB7Cs2nRPu0&e=> service to which a packet should be sent.

BIER forwarding seems match very much a “network layer service” in my opinion, and the “AB37” in “2019::AB37” is very similar to a NSEL too.

Thanks
Jingrong


From: Antoni Przygienda [mailto:prz@juniper.net]
Sent: Friday, July 12, 2019 12:02 AM
To: Jeffrey (Zhaohui) Zhang <zzhang@juniper.net<mailto:zzhang@juniper.net>>; Xiejingrong <xiejingrong@huawei.com<mailto:xiejingrong@huawei.com>>; draft-zhang-bier-bierin6@ietf.org<mailto:draft-zhang-bier-bierin6@ietf.org>; BIER WG <bier@ietf.org<mailto:bier@ietf.org>>
Subject: Re: Questions regarding <draft-zhang-bier-bierin6-03>


2.1.  IPv6 Options Considerations

   RFC 8200 section 4, defines the IPv6 extension headers.  Currently
   there are two defined extension headers, Hop-by-Hop and Destination
   options header, which can carry a variable number of options.  These
   extension headers are inserted by the source node.

   For directly connected BIER routers, IPv6 Hop-by-Hop or Destination
   options are irrelevant and SHOULD NOT be inserted by BFIR on the
   BIERin6 packet.  In this case IPv6 header, Next Header field should
   be set to TBD.  Any IPv6 packet arriving on BFRs and BFERs, with
   multiple extension header where the last extension header has a Next
   Header field set to TBD, SHOULD be discard and the node should
   transmit an ICMP Parameter Problem message to the source of the
   packet (BFIR) with an ICMP code value of TBD10 ('invalid options for
   BIERin6').
[XJR Q6]: You have to walk the ext header chain and get the last NH to judge if this packet need to be discard, right? For example for an incoming packet(ipv6hdr+RoutingHeader+DestOptHdr<nh!=TBD>), you have to walk the whole extension header chain until you know the last NH, to execute the above “discard” action. Right?


prz> topic for discussion. The whole v6 options consideration is basically a first stab.

   This also indicates that for disjoint BIER routers using IPv6
   encapsulation, there SHOULD NOT be any IPv6 Hop-by-Hop or Destination
   options be present in a BIERin6 packet.
[XJR Q7]: What does “disjoint BIER router” mean?

prz> non-adjacent, good catch




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