FRR BGP协议分析8 -- BGP 层3隧道 (2)

布满荆棘的人生 2023-06-17 05:55 180阅读 0赞

# 本文，我们分析UPDATE消息的处理过程 #

层3VPN 的UPDATE消息和前面的路由更新报文的接受处理是一样的，从解析属性的地方开始区别，报文如下图：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70][]

2019/12/26 09:32:44 BGP: : 20.20.20.20 rcvd UPDATE w/ attr: , origin ?, metric 100, extcommunity RT:12.1.1.2:2, path 200

2019/12/26 09:32:44 BGP: : 20.20.20.20 rcvd UPDATE wlen 0 attrlen 69 alen 0

2019/12/26 09:32:44 BGP: : 20.20.20.20 rcvd RD 12.1.1.2:2 1.1.1.1/32 label 154 IPv4 vpn

2019/12/26 09:32:44 BGP: : vpn\_leak\_to\_vrf\_update: start (path\_vpn=0x5589ff3debf0)

2019/12/26 09:32:44 BGP: : vpn\_leak\_to\_vrf\_update\_onevrf: skipping: import not set

2019/12/26 09:32:44 BGP: : vpn\_leak\_to\_vrf\_update\_onevrf: updating 1.1.1.1/32 to vrf VRF 1

2019/12/26 09:32:44 BGP: : vpn\_leak\_to\_vrf\_update\_onevrf: pfx 1.1.1.1/32: num\_labels 1

2019/12/26 09:32:44 BGP: : leak\_update: entry: leak-to=VRF 1, p=1.1.1.1/32, type=9, sub\_type=0

2019/12/26 09:32:44 BGP: : leak\_update: nexthop is valid (in vrf VRF default)

2019/12/26 09:32:44 BGP: : leak\_update: ->VRF 1: 1.1.1.1/32: Added new route

2019/12/26 09:32:44 BGP: : group\_announce\_route\_walkcb: afi=IPv4, safi=vpn, p=1.1.1.1/32

2019/12/26 09:32:44 BGP: : subgroup\_process\_announce\_selected: p=1.1.1.1/32, selected=0x5589ff3debf0

2019/12/26 09:32:44 BGP: : bgp\_zebra\_announce: p=1.1.1.1/32, bgp\_is\_valid\_label: 2

2019/12/26 09:32:44 BGP: : Tx route add VRF 7 1.1.1.1/32 metric 100 tag 0 count 1

2019/12/26 09:32:44 BGP: :   nhop \[1\]: 20.20.20.20 if 0 VRF 0 label 154

2019/12/26 09:32:44 BGP: : bgp\_zebra\_announce: 1.1.1.1/32: announcing to zebra (recursion set)

2019/12/26 09:32:44 BGP: : u11:s11 send UPDATE w/ attr: , origin ?, extcommunity RT:12.1.1.2:2, path 200

2019/12/26 09:32:44 BGP: : u11:s11 send MP\_REACH for afi/safi 1/128

2019/12/26 09:32:44 BGP: : u11:s11 send UPDATE RD 12.1.1.2:2 1.1.1.1/32 label 154 IPv4 vpn

2019/12/26 09:32:44 BGP: : u11:s11 send UPDATE len 89 numpfx 1

2019/12/26 09:32:44 BGP: : u11:s11 20.20.20.20 send UPDATE w/ nexthop 10.10.10.10 and RD

# 属性解析 #

在属性解析函数 bgp\_attr\_parse里面，我们分析和层3隧道相关的属性解析。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 1][]

**解析MP\_REACH\_NLRI**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 2][]

*  首先解析报文的afi和safi的值为1和128，然后转化为FRR 内部自己定义的afi和safi的值。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 3][]

*  解析下一跳

获取下一跳的长度为12，然后获取RD(8字节)，但没有存储，只是跳过，在获取IP地址4字节，存放在attr下一跳nexthop里面。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 4][]

![20191128160252128.png][]

最后存放在bgp\_nlri的NLRI\_MP\_UPDATE里面，nlri保存的是MP\_REACH\_NLRI信息。

**解析EXT\_COMMUNITIES**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 5][]

# NLRI处理 #

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 6][]

bgp\_nlri\_parse 函数里面由于前面解析的safi是SAFI\_MPLS\_VPN，所以NLRI的处理会是bgp\_nlri\_parse\_vpn函数，主要处理过程如下，可以结合上面的报文一起看代码处理过程：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 7][]

bgp\_update 前面分析的时候，大概过程已经分析过了，下面会分析下，前面忽略的L3VPN相关的处理过程。

*  has\_valid\_label处理会变成1，因为前面传入了解析出来的label值

![20191128160328680.png][]

*  在构建struct bgp\_path\_info的时候，如果label有值，还需要构建struct bgp\_path\_info\_extra，然后把label值存放在info\_extra里面

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 8][]

![20191128160414431.png][]

*  把路由信息导入到VRF的BGP里面

![20191128160422745.png][]

vpn\_leak\_to\_vrf\_update 函数处理有点长，主体处理的是把vpn peer收到的路由信息，导入到VRF的BGP里面

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 9][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 10][]

# 发送端ospf vrf的路由导入BGP处理： #

**Zebra:**

ubuntu\# 2019/12/26 13:05:00 ZEBRA: : netlink\_parse\_info: netlink-listen (NS 0) type RTM\_NEWNEIGH(28), len=76, seq=0, pid=0

2019/12/26 13:05:00 ZEBRA: :    Neighbor Entry received is not on a VLAN or a BRIDGE, ignoring

2019/12/26 13:05:00 ZEBRA: : netlink\_parse\_info: netlink-listen (NS 0) type RTM\_NEWNEIGH(28), len=76, seq=0, pid=0

2019/12/26 13:05:00 ZEBRA: :    Neighbor Entry received is not on a VLAN or a BRIDGE, ignoring

2019/12/26 13:05:08 ZEBRA: : zebra message\[ZEBRA\_ROUTE\_ADD:7:45\] comes from socket \[42\]

2019/12/26 13:05:08 ZEBRA: : Read 1 packets from client: ospf

2019/12/26 13:05:08 ZEBRA: : rib\_add\_multipath: 7:1.1.1.1/32: Inserting route rn 0x56275b8132b0, re 0x56275b812140 (ospf) existing (nil)

2019/12/26 13:05:08 ZEBRA: : rib\_add\_multipath: dumping RE entry 0x56275b812140 for 1.1.1.1/32 vrf 7

2019/12/26 13:05:08 ZEBRA: : 1.1.1.1/32: uptime == 118014, type == 6, instance == 0, table == 1

2019/12/26 13:05:08 ZEBRA: : 1.1.1.1/32: metric == 100, mtu == 0, distance == 110, flags == 0, status == 0

2019/12/26 13:05:08 ZEBRA: : 1.1.1.1/32: nexthop\_num == 1, nexthop\_active\_num == 0

2019/12/26 13:05:08 ZEBRA: : 1.1.1.1/32: NH 12.1.1.1\[5\] vrf 1(7) with flags

2019/12/26 13:05:08 ZEBRA: : 1.1.1.1/32: dump complete

2019/12/26 13:05:08 ZEBRA: : rib\_link: 7:1.1.1.1/32: rn 0x56275b8132b0 adding dest

2019/12/26 13:05:08 ZEBRA: : rib\_meta\_queue\_add: 7:1.1.1.1/32: queued rn 0x56275b8132b0 into sub-queue 2

2019/12/26 13:05:08 ZEBRA: : 7:1.1.1.1/32: Processing rn 0x56275b8132b0

2019/12/26 13:05:08 ZEBRA: : 7:1.1.1.1/32: Examine re 0x56275b812140 (ospf) status 2 flags 0 dist 110 metric 100

2019/12/26 13:05:08 ZEBRA: : 7:1.1.1.1/32: After processing: old\_selected 0x0 new\_selected 0x56275b812140 old\_fib 0x0 new\_fib 0x56275b812140

2019/12/26 13:05:08 ZEBRA: : 7:1.1.1.1/32: Adding route rn 0x56275b8132b0, re 0x56275b812140 (ospf)

2019/12/26 13:05:08 ZEBRA: : netlink\_route\_multipath(): RTM\_NEWROUTE 1.1.1.1/32 vrf 7(1)

2019/12/26 13:05:08 ZEBRA: : netlink\_route\_multipath() (single-path): nexthop via 12.1.1.1  if 5(7)

2019/12/26 13:05:08 ZEBRA: : netlink\_talk: netlink-dp (NS 0) type RTM\_NEWROUTE(24), len=60 seq=115 flags 0x501

2019/12/26 13:05:08 ZEBRA: : 7:1.1.1.1/32: rn 0x56275b8132b0 dequeued from sub-queue 2

2019/12/26 13:05:08 ZEBRA: : update\_from\_ctx: 7:1.1.1.1/32: SELECTED

2019/12/26 13:05:08 ZEBRA: : 7:1.1.1.1/32 update\_from\_ctx(): no fib nhg

2019/12/26 13:05:08 ZEBRA: : 7:1.1.1.1/32 update\_from\_ctx(): rib nhg matched, changed 'true'

2019/12/26 13:05:08 ZEBRA: : 7:1.1.1.1/32: Redist update re 0x56275b812140 (ospf), old 0x0 (None)

2019/12/26 13:05:08 ZEBRA: : zsend\_redistribute\_route: ZEBRA\_REDISTRIBUTE\_ROUTE\_ADD to client bgp: type ospf, vrf\_id 7, p 1.1.1.1/32

2019/12/26 13:05:08 ZEBRA: : Not Notifying Owner: 6 about prefix 1.1.1.1/32(1) 2 vrf: 7

**Bgp:**

ubuntu\# 2019/12/26 13:05:08 BGP: : vpn\_leak\_from\_vrf\_update: from vrf VRF 1

2019/12/26 13:05:08 BGP: : vpn\_leak\_from\_vrf\_update: post merge static\_attr.ecommunity\{12.1.1.2:2\}

2019/12/26 13:05:08 BGP: : vpn\_leak\_from\_vrf\_update: new\_attr->ecommunity\{12.1.1.2:2\}

2019/12/26 13:05:08 BGP: : leak\_update: entry: leak-to=VRF default, p=1.1.1.1/32, type=6, sub\_type=3

2019/12/26 13:05:08 BGP: : leak\_update: nexthop is valid (in vrf VRF 1)

2019/12/26 13:05:08 BGP: : leak\_update: ->VRF default: 1.1.1.1/32: Added new route

2019/12/26 13:05:08 BGP: : vpn\_leak\_to\_vrf\_update: start (path\_vpn=0x557deca2fe90)

2019/12/26 13:05:08 BGP: : vpn\_leak\_to\_vrf\_update\_onevrf: skipping: import not set

2019/12/26 13:05:08 BGP: : Rx route ADD VRF 7 ospf\[0\] 1.1.1.1/32 nexthop 12.1.1.1 (type 3 if 5) metric 100 tag 0

2019/12/26 13:05:08 BGP: : group\_announce\_route\_walkcb: afi=IPv4, safi=vpn, p=1.1.1.1/32

2019/12/26 13:05:08 BGP: : subgroup\_process\_announce\_selected: p=1.1.1.1/32, selected=0x557deca2fe90

2019/12/26 13:05:08 BGP: : u4:s4 send UPDATE w/ attr: nexthop 0.0.0.0, metric 100, extcommunity RT:12.1.1.2:2, originator 2.2.2.2, path

2019/12/26 13:05:08 BGP: : u4:s4 send MP\_REACH for afi/safi 1/128

2019/12/26 13:05:08 BGP: : u4:s4 send UPDATE RD 12.1.1.2:2 1.1.1.1/32 label 154 IPv4 vpn

2019/12/26 13:05:08 BGP: : u4:s4 send UPDATE len 92 numpfx 1

2019/12/26 13:05:08 BGP: : u4:s4 10.10.10.10 send UPDATE w/ nexthop 20.20.20.20 and RD

2019/12/26 13:05:08 BGP: : 10.10.10.10 rcvd UPDATE w/ attr: , origin ?, extcommunity RT:12.1.1.2:2, path 100 200

2019/12/26 13:05:08 BGP: : 10.10.10.10 rcvd UPDATE wlen 0 attrlen 66 alen 0

2019/12/26 13:05:08 BGP: : 10.10.10.10 rcvd UPDATE about RD 12.1.1.2:2 1.1.1.1/32 label 154 IPv4 vpn -- DENIED due to: as-path contains our own AS;

Bgp端的函数subgroup\_update\_packet构造的update报文发送

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 11][]

发送的时候如果报文里面nexthop属性为0的话，bpacket\_reformat\_for\_peer 这个函数会改nexthop的IP地址

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20191226174026123.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c=,size_16,color_FFFFFF,t_70
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c_size_16_color_FFFFFF_t_70 4]: https://img-blog.csdnimg.cn/20191128160237155.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FybWxpbnV4d3c=,size_16,color_FFFFFF,t_70
[20191128160252128.png]: https://img-blog.csdnimg.cn/20191128160252128.png
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[20191128160328680.png]: https://img-blog.csdnimg.cn/20191128160328680.png
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[20191128160414431.png]: https://img-blog.csdnimg.cn/20191128160414431.png
[20191128160422745.png]: https://img-blog.csdnimg.cn/20191128160422745.png
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