diff --git a/ipam/allocate.go b/ipam/allocate.go
index ac542aac..c4092a12 100644
--- a/ipam/allocate.go
+++ b/ipam/allocate.go
@@ -14,9 +14,9 @@ type allocateResult struct {
 
 type allocate struct {
 	resultChan       chan<- allocateResult
-	ident            string
+	ident            string       // a container ID, something like "weave:expose", or api.NoContainerID
 	r                address.CIDR // Subnet we are trying to allocate within
-	isContainer      bool
+	isContainer      bool         // true if ident is a container ID
 	hasBeenCancelled func() bool
 }
 
diff --git a/ipam/allocator.go b/ipam/allocator.go
index 71b21309..6ad7a540 100644
--- a/ipam/allocator.go
+++ b/ipam/allocator.go
@@ -76,9 +76,10 @@ type Allocator struct {
 	now               func() time.Time
 }
 
+// PreClaims are IP addresses discovered before we could initialize IPAM
 type PreClaim struct {
-	Ident       string
-	IsContainer bool
+	Ident       string // a container ID, something like "weave:expose", or api.NoContainerID
+	IsContainer bool   // true if Ident is a container ID
 	Cidr        address.CIDR
 }
 
diff --git a/ipam/claim.go b/ipam/claim.go
index dfd3ab76..9a827e54 100644
--- a/ipam/claim.go
+++ b/ipam/claim.go
@@ -12,10 +12,10 @@ import (
 
 type claim struct {
 	resultChan       chan<- error
-	ident            string
-	cidr             address.CIDR
-	isContainer      bool
-	noErrorOnUnknown bool
+	ident            string       // a container ID, something like "weave:expose", or api.NoContainerID
+	cidr             address.CIDR // single address being claimed
+	isContainer      bool         // true if ident is a container ID
+	noErrorOnUnknown bool         // if false, error or block if we don't know; if true return ok but keep trying
 	hasBeenCancelled func() bool
 }