diff --git a/src/system/ether.1 b/src/system/ether.1
index c43abf51..68a69eee 100644
--- a/src/system/ether.1
+++ b/src/system/ether.1
@@ -251,6 +251,8 @@ ETHTXI:
 	PUSH P,E
 	PUSH P,I
 	PUSH P,R
+	PUSH P,Q
+	PUSH P,T
 
 	; Search the ARP table for the destination address.
 	MOVE C,PK.DST(A)
@@ -304,7 +306,12 @@ ETHTX2:				;Not found in ARP table
 
 	MOVEI R,ETHABF		;Data pointer
 	MOVEI I,%NEAH"LENGTH	;Length in bytes
-	JRST ETHTX5		;Send it!
+	PUSHJ P,ETHTX		;Send it!
+	 JFCL			; Can't send - oh well, we'll try again later
+	JRST ETHTX5
+
+	; As we've sent an ARP request instead of the packet we actually
+	; wanted to send, don't call IPIODN.
 
 ETHTX3:				;Found MAC in ARP table
 	; Found the destination address in the ARP table. Send it!
@@ -323,8 +330,16 @@ ETHTX3:				;Found MAC in ARP table
 
 	MOVE R,PK.BUF(A)	;Data pointer
 	LDB I,[IP$TOL(R)]	;Length in bytes, from the IP header
-ETHTX5:	PUSHJ P,ETHTX		;Send it!
+	PUSH P,A
+	PUSHJ P,ETHTX		;Send it!
+	 JRST [	POP P,A		;Couldn't send - don't mark as done.
+		JRST ETHTX5]
 
+	POP P,A
+	PUSHJ P,IPIODN		;Tell IP we've sent this one.
+
+ETHTX5:	POP P,T
+	POP P,Q
 	POP P,R
 	POP P,I
 	POP P,E
@@ -338,11 +353,12 @@ ETHTX5:	PUSHJ P,ETHTX		;Send it!
 ;Unpacked header is in ETHHBF. R contains pointer to unpacked data.
 ;I contains data length in bytes.
 ;Clobbers A, B, C, TT, I.
+;Skip-returns on success; normal return on failure.
 ;
 ;FIXME IFN UNAP,...
 ETHTX:	BUG INFO,[ethtx ptr ],OCT,R,[ len ],OCT,I
 	PUSHJ P,UNAFF			;Find a free transmit buffer
-	 POPJ P,			;None left. Give up.
+	 POPJ P,			;None left. Fail.
 	;BUG INFO,[ethtx buf ],OCT,B,[ desc ],OCT,D,[ len ],OCT,I
 
 	MOVE TT,B			;Convert header
@@ -362,6 +378,7 @@ ETHTX:	BUG INFO,[ethtx ptr ],OCT,R,[ len ],OCT,I
 
 	ADDI I,%NEH"LENGTH-%NEH"PAD	;Add length of header
 	BUG INFO,[ethtx end desc ],OCT,D,[ len ],OCT,I
+	AOS (P)				;Success - skip return
 	JRST UNATX			;Transmit it
 
 ;Check whether the interface is able to send a packet.
@@ -648,6 +665,7 @@ UNABRK:	0
 
 	;FIXME %UN0"TXI
 
+;FIXME simh's code to assert RCBI is commented out...
 	TRNE H,%UN0"RCBI
 	 SETOM UNARCB		;Just remember for when a buffer is freed
 
@@ -675,8 +693,10 @@ UNARX1:	HRRZ A,W		;Wrap index around
 	 HLLZS W
 
 	HLRZ J,UNRXRP(W)	;Descriptor
+	HRRZ I,UNRXRP(W)	;XXX unibus
 
 	MOVE Q,1(J)		;Is there a packet in this buffer? (OWN=0)
+	BUG INFO,[rx check buffer J=],OCT,J,[ unibus ],OCT,I,[ flags Q=],OCT,Q
 	TLNE Q,%UNTD"OWN
 	 JRST [	SKIPGE UNRXRI	;No. First empty buffer we've found?
 		 HRRZM W,UNRXRI	; Yes, start here next time
@@ -694,8 +714,11 @@ UNARX1:	HRRZ A,W		;Wrap index around
 	SUBI I,4		;Ignore CRC at end
 	PUSHJ P,ETHRX
 
+	BUG INFO,[rx after ethrx buffer J=],OCT,J,[ flags Q=],OCT,Q
+
 UNARX3:	TLO Q,%UNTD"OWN		;Set OWN=1 to mark as free
 	MOVEM Q,1(J)
+	BUG INFO,[rx set own=1 for ],OCT,J
 
 	SKIPE UNARCB		;Have we had an RCB interrupt?
 	 JRST [	SETZM UNARCB	;Yes. Tell the DEUNA there's a free buffer now.
diff --git a/src/system/tcp.275 b/src/system/tcp.275
index f518d7c3..c9cc1fec 100755
--- a/src/system/tcp.275
+++ b/src/system/tcp.275
@@ -1094,6 +1094,13 @@ SUBTTL TCP Main Program Output
 TCPW:	 MOVEI A,CHRKT
 	METER("TCP: syscal out")
 	HLRZ I,(R)		; Get TCB index from IOCHNM wd
+	PUSH P,D
+	PUSH P,E
+	MOVE D,XBORTL(I)
+	UMOVE E,(C) ;XXX user's count
+	BUG INFO,[tcpw TCB index=],OCT,I,[ count=],OCT,E,[ rtq len=],OCT,D
+	POP P,E
+	POP P,D
 
 	; Verify state, do misc setup for writing, lock segment.
 	CONO PI,NETOFF
@@ -3239,6 +3246,10 @@ TSOSND:	MOVSI T,(TC%ACK)	; Simple data segment
 ;	IP$PTC - Protocol number (needn't set, assumes %PTCTC always)
 
 TSOSN:	METER("TCP: Out segs")
+	PUSH P,A
+	MOVE A,TT
+	BUG INFO,[tsosn index=],OCT,I,[ sending bytes=],OCT,A
+	POP P,A
 	AND T,[TH%CTL]		; Ensure non-flag bits are flushed.
 	MOVE A,T
 	ANDCAB A,XBSTAT(I)		; Turn off these request bits
@@ -3314,6 +3325,10 @@ TSOSN2:	LDB A,[PK$TDO (R)]		; Bytes of header
 	ADD TT,XBSNXT(I)		; Get new SND.NXT
 	TLZ TT,%MOD32
 	MOVEM TT,XBSNXT(I)
+	PUSH P,A
+	MOVE A,TT
+	BUG INFO,[tsosn new snd.nxt=],OCT,A
+	POP P,A
 	SKIPN XBORTT(I)			; Retrans timeout already set?
 	 JRST [	MOVE A,TIME
 		ADD A,TCPTMO		; Make it 5 sec for now.
@@ -3326,7 +3341,11 @@ TSOSN2:	LDB A,[PK$TDO (R)]		; Bytes of header
 	CALL PKQPL(PK.TCP)		; Put on TCP retrans queue
 	AOS XBORTL(I)			; Bump count of segs on queue
 
-TSOSN8:	CALL IPKSND			; Put on IP output queue
+TSOSN8:	PUSH P,A
+	MOVE A,XBORTL(I)
+	BUG INFO,[tsosn8 sending index=],OCT,I,[ rtq len=],OCT,A
+	POP P,A
+	CALL IPKSND			; Put on IP output queue
 	RET
 
 SUBTTL TCP Retransmit and Timeout