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Class-Based Forwarding latest model (opencomputeproject#1193)
This PR defines class-based forwarding. It contains two aspects: Assignment of a Forwarding Class to a packet, via QOS map or ACL New next-hop group type: SAI_NEXT_HOP_GROUP_TYPE_CLASS_BASED Where member selection is based on the forwarding-class of the packet. Signed-off-by: Jason Bos <jbos@cisco.com>
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| # Class-based Forwarding | ||
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| Title | Class-based Forwarding | ||
| ------------|---------------- | ||
| Authors | Cisco | ||
| Status | In review | ||
| Type | Standards track | ||
| Created | 04/14/2021 | ||
| SAI-Version | 1.8 | ||
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| Class-based forwarding provides a method to steer traffic among multiple paths through the network by policy rather than, or in combination with, traditional ECMP/UCMP flow-hashing. | ||
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| A new type of next-hop group is introduced: | ||
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| ``` | ||
| typedef enum _sai_next_hop_group_type_t | ||
| { | ||
| ... | ||
| /** Next hop group is class-based, with members selected by Forwarding class */ | ||
| SAI_NEXT_HOP_GROUP_TYPE_CLASS_BASED, | ||
| ... | ||
| } sai_next_hop_group_type_t; | ||
| ``` | ||
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| The behavior of SAI_NEXT_HOP_GROUP_TYPE_CLASS_BASED differs from the traditional SAI_NEXT_HOP_GROUP_TYPE_ECMP, in that each packet will have a Forwarding class that chooses next-hop group member index. | ||
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| This is accomplished by directly mapping each forwarding class to the group member index, via map configured to the next-hop group object. | ||
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| ``` | ||
| /** | ||
| * @brief Member selection map | ||
| * | ||
| * @type sai_object_id_t | ||
| * @flags CREATE_AND_SET | ||
| * @objects SAI_OBJECT_TYPE_NEXT_HOP_GROUP_MAP | ||
| * @allownull true | ||
| * @default SAI_NULL_OBJECT_ID | ||
| * @validonly SAI_NEXT_HOP_GROUP_ATTR_TYPE == SAI_NEXT_HOP_GROUP_TYPE_CLASS_BASED | ||
| */ | ||
| SAI_NEXT_HOP_GROUP_ATTR_SELECTION_MAP, | ||
| ``` | ||
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| If a packet arrives with a forwarding-class which is not present in the map, the chosen index shall be 0. | ||
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| ``` | ||
| typedef enum _sai_next_hop_group_member_attr_t | ||
| { | ||
| ... | ||
| /** | ||
| * @brief Object index in the next-hop group. | ||
| * | ||
| * Index specifying the strict member's order. | ||
| * Allowed value range for is from 0 to SAI_NEXT_HOP_GROUP_ATTR_REAL_SIZE - 1. | ||
| * Should only be used if the type of owning group is SAI_NEXT_HOP_GROUP_TYPE_FINE_GRAIN_ECMP | ||
| * or SAI_NEXT_HOP_GROUP_TYPE_CLASS_BASED. | ||
| * | ||
| * @type sai_uint32_t | ||
| * @flags CREATE_ONLY | ||
| * @default 0 | ||
| */ | ||
| SAI_NEXT_HOP_GROUP_MEMBER_ATTR_INDEX, | ||
| ... | ||
| } sai_next_hop_group_member_attr_t; | ||
| ``` | ||
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| If the map selects an index for which a member does not exist, the packet shall be treated as having a next-hop of SAI_NULL_OBJECT_ID, dropping the packet. | ||
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| Members of type next-hop or next-hop groups of type ECMP shall be allowed. To allow this, next-hop group member type is extended to allow other next-hop groups: | ||
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| ``` | ||
| /** | ||
| * @brief Next hop id | ||
| * | ||
| * @type sai_object_id_t | ||
| * @flags MANDATORY_ON_CREATE | CREATE_AND_SET | ||
| * @objects SAI_OBJECT_TYPE_NEXT_HOP, <b>SAI_OBJECT_TYPE_NEXT_HOP_GROUP</b> | ||
| */ | ||
| SAI_NEXT_HOP_GROUP_MEMBER_ATTR_NEXT_HOP_ID, | ||
| ``` | ||
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| *Note: While this would also be a means to configure a hierarchical ECMP, hierarchical ECMP is outside the scope of this proposal.* | ||
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| The forwarding-class for a packet may be selected via qos-map or ACL. | ||
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| ``` | ||
| typedef enum _sai_qos_map_type_t | ||
| { | ||
| ... | ||
| /** QOS Map to set DSCP to Forwarding class */ | ||
| SAI_QOS_MAP_TYPE_DSCP_TO_FORWARDING_CLASS = 0x0000000d, | ||
| /** QOS Map to set EXP to Forwarding class */ | ||
| SAI_QOS_MAP_TYPE_MPLS_EXP_TO_FORWARDING_CLASS = 0x0000000e, | ||
| ... | ||
| } sai_qos_map_type_t; | ||
| ``` | ||
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| ``` | ||
| typedef enum _sai_acl_entry_attr_t | ||
| ... | ||
| /** | ||
| * @brief Set Forwarding Class | ||
| * | ||
| * @type sai_acl_action_data_t sai_uint8_t | ||
| * @flags CREATE_AND_SET | ||
| * @default disabled | ||
| */ | ||
| SAI_ACL_ENTRY_ATTR_ACTION_SET_FORWARDING_CLASS, | ||
| ... | ||
| } sai_acl_entry_attr_t; | ||
| ``` | ||
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| If the packet is not assigned a forwarding-class, then the forwarding-class of the packet shall be 0. For example, if no qos-map or ACL is configured. Normal QOS/ACL precedence rules apply; if supported by the implementation, the ACL would override the QOS MAP decision. | ||
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| *Resource monitoring considerations:* | ||
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| The attribute SAI_SWITCH_ATTR_MAX_NUMBER_OF_FORWARDING_CLASSES may be used to identify the maximum forwarding-class allowed. | ||
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| The SAI_OBJECT_TYPE_NEXT_HOP_GROUP_MAP object is a resource. The sai_object_type_get_availability() API may be used to query the maximum number of permitted maps. | ||
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| *Class-based forwarding group configuration example:* | ||
| ``` | ||
| /****************************************************** | ||
| * Create a forwarding-class -> index map. | ||
| * In this example, map 8 forwarding-classes to 2 members. | ||
| * FC 0-5 -> index 0 | ||
| * FC 6-7 -> index 1 | ||
| ******************************************************/ | ||
| const int num_forwarding_classes = 8; | ||
| const int num_members = 2; | ||
| sai_object_id_t nh_group_map; | ||
| sai_map_t fc_map[num_forwarding_classes]; | ||
| for (int fc = 0; fc < num_forwarding_classes; ++fc) { | ||
| fc_map[fc].key = fc; | ||
| if (fc >= 6) { | ||
| fc_map[fc].value = 1; | ||
| } else { | ||
| fc_map[fc].value = 0; | ||
| } | ||
| } | ||
| sai_map_list_t fc_map_list; | ||
| fc_map_list.key.count = num_forwarding_classes; | ||
| fc_map_list.key.list = fc_map; | ||
| attr.id = SAI_NEXT_HOP_GROUP_MAP_ATTR_TYPE; | ||
| attr.value.u32 = SAI_NEXT_HOP_GROUP_MAP_TYPE_FORWARDING_CLASS_TO_INDEX; | ||
| attrs.push_back(attr); | ||
| attr.id = SAI_NEXT_HOP_GROUP_MAP_ATTR_MAP_TO_VALUE_LIST; | ||
| attr.value.maplist = fc_map_list; | ||
| attrs.push_back(attr); | ||
| sai_next_hop_group_api->create_next_hop_group_map( | ||
| &nh_group_map, | ||
| g_switch_id, | ||
| attrs.size(), | ||
| attrs.data()); | ||
| /***************************************************** | ||
| * Create a class-based forwarding group | ||
| *****************************************************/ | ||
| attrs.clear(); | ||
| sai_object_id_t nh_group; | ||
| attr.id = SAI_NEXT_HOP_GROUP_ATTR_TYPE; | ||
| attr.value.u32 = SAI_NEXT_HOP_GROUP_TYPE_CLASS_BASED; | ||
| attrs.push_back(attr); | ||
| attr.id = SAI_NEXT_HOP_GROUP_ATTR_CONFIGURED_SIZE; | ||
| attr.value.u32 = num_members; | ||
| attrs.push_back(attr); | ||
| attr.id = SAI_NEXT_HOP_GROUP_ATTR_SELECTION_MAP; | ||
| attr.value.oid = nh_group_map; | ||
| attrs.push_back(attr); | ||
| sai_next_hop_group_api->create_next_hop_group( | ||
| &nh_group, | ||
| g_switch_id, | ||
| attrs.size(), | ||
| attrs.data()); | ||
| /***************************************************** | ||
| * Create members | ||
| *****************************************************/ | ||
| attrs.clear(); | ||
| for (index = 0; index < num_members; ++index) { | ||
| attr.id = SAI_NEXT_HOP_GROUP_MEMBER_ATTR_NEXT_HOP_GROUP_ID; | ||
| attr.value.oid = nh_group; | ||
| attrs.push_back(attr); | ||
| attr.id = SAI_NEXT_HOP_GROUP_MEMBER_ATTR_NEXT_HOP_ID; | ||
| attr.value.oid = destinations[index]; // Next-hop or ECMP group | ||
| attrs.push_back(attr); | ||
| attr.id = SAI_NEXT_HOP_GROUP_MEMBER_ATTR_INDEX; | ||
| attr.value.u32 = index; | ||
| attrs.push_back(attr); | ||
| sai_next_hop_group_api->create_next_hop_group_member( | ||
| &members[member_index], | ||
| g_switch_id, | ||
| attrs.size(), | ||
| attrs.data()); | ||
| } | ||
| ``` |
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