Tofino 交换机基础实验: Simple Forward¶
在本节中，实验者将学习如何在真实 Tofino 芯片交换机上进行 L2/L3 Forwarding 实验，熟悉硬件架构和适配 Tofino 的 P4 编程方法，实现从仿真环境到真实硬件的过渡
在本节中，将以 simple_forward程序为例，帮助实验者将了解如何在 Tofino 芯片交换机上编译、运行 P4 程序，如何通过 bfshell 下发表项等。
在 simple_forward 程序中，交换机实现了基于端口号的 Forwarding 功能，实验者可以通过 bfshell 手动下发表项，实现两个端口之间的互通
action ai_forward(portid_t egress_port){
ig_tm_md.ucast_egress_port = egress_port;
}
table ti_forward{
key = {
ig_intr_md.ingress_port: exact;
}
actions = {
ai_forward;
ai_drop;
}
size = 1024;
default_action = ai_drop;
}
以下部分讲解如何通过 bfshell ⼿动下发表项
通过 bfshell ⼿动下发表项¶
程序编译¶
可参考学习 Makefile 中的编译指令
# 登录 root 用户
cd ~/simple_forward
make
编译好后的程序会在 /root/bf-sde-9.13.0/build/p4-build/tofino/simple_forward/
程序运行¶
/root/bf-sde-9.13.0/run_switchd.sh -p simple_forward
运行截图如下，出现 bfshell> 证明成功运行
端口开启¶
运行以上指令进入 bfshell 后，进入 ucli 模式开启端口：
bfshell> ucli
Starting UCLI from bf-shell
Cannot read termcap database;
using dumb terminal settings.
bf-sde> xcvr_pres_ignore 9/- 1
bf-sde> xcvr_los_ignore 9/- 1
bf-sde> pm
bf-sde.pm> port-add 9/0 10G NONE
bf-sde.pm> port-add 9/1 10G NONE
bf-sde.pm> port-enb 9/0
bf-sde.pm> port-enb 9/1
bf-sde.pm> show
-----+----+---+----+-------+----+--+--+---+---+---+--------+----------------+----------------+-
PORT |MAC |D_P|P/PT|SPEED |FEC |AN|KR|RDY|ADM|OPR|LPBK |FRAMES RX |FRAMES TX |E
-----+----+---+----+-------+----+--+--+---+---+---+--------+----------------+----------------+-
9/0 |23/0|132|3/ 4|10G |NONE|Au|Au|YES|ENB|UP | NONE | 5| 0|
9/1 |23/1|133|3/ 5|10G |NONE|Au|Au|YES|ENB|UP | NONE | 2| 0|
bf-sde.pm>
表项下发¶
使用 exit 指令退回⾄ bfshell，运⾏ bfrt_python，使用 bfrt.info() 查看当前表项：
bf-sde.pm> exit
bfshell> bfrt_python
cwd : /root/simple_forward
We've found 1 p4 programs for device 0:
simple_forward
Creating tree for dev 0 and program simple_forward
Devices found : [0]
Python 3.10.9 (main, Oct 6 2024, 07:19:08) [GCC 9.4.0]
Type 'copyright', 'credits' or 'license' for more information
IPython 7.31.1 -- An enhanced Interactive Python. Type '?' for help.
bfrt_python> bfrt.info()
Tables under this node:
Full Table Name Type Usage Capacity
--------------------------------------- -------------------------- ------- ----------
tbl_dbg_counter DBG_CNT 192 192
pipe.snapshot.ingress_trigger SNAPSHOT_TRIG n/a 12
pipe.snapshot.ingress_liveness SNAPSHOT_LIVENESS n/a 0
pipe.snapshot.ingress_data SNAPSHOT_DATA 12 12
pipe.snapshot.egress_trigger SNAPSHOT_TRIG n/a 12
pipe.snapshot.egress_liveness SNAPSHOT_LIVENESS n/a 0
pipe.snapshot.egress_data SNAPSHOT_DATA 12 12
pipe.snapshot.cfg SNAPSHOT_CFG 0 12
pipe.SwitchIngressParser.$PORT_METADATA PORT_METADATA 0 288
pipe.SwitchIngress.ti_forward MATCH_DIRECT 0 1024
......
可以看到 pipe.SwitchIngress.ti_forward 是我们数据平⾯程序的表
bfrt_python使用 tips: 想查看的表后加?可以查看针对该表可以进⾏什么操作，例如bfrt?
接下来我们重点关注 pipe.SwitchIngress.ti_forward
bfrt_python> tbl = bfrt.simple_forward.pipe.SwitchIngress.ti_forward
bfrt_python> tbl.info()
......
bfrt_python> tbl?
......
bfrt_python> tbl.add_with_ai_forward?
Help on method add_with_ai_forward in module bfrtcli:
add_with_ai_forward(ingress_port=None, egress_port=None, pipe=None, gress_dir=None, prsr_id=None) method of bfrtcli.BFLeaf instance
Add entry to ti_forward table with action: SwitchIngress.ai_forward
Parameters:
ingress_port type=EXACT size=9 default=0
egress_port type=BYTE_STREAM size=9 default=0
经过 tbl? 我们查询到 add_with_ai_forward 是一个添加 ai_forward 动作表项的下发接口
通过以下指令即可下发两个端口的表项：
tbl.add_with_ai_forward(
ingress_port=132,
egress_port=133
)
tbl.add_with_ai_forward(
ingress_port=133,
egress_port=132
)
以上即为手动下发表项的参考，更快速、更复杂的下发表项的办法请参考提供的 simple_forward 示例程序